Document:

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                                                                 Exhibit 10.1.8

THE SECURITIES EVIDENCED BY THIS WARRANT CERTIFICATE HAVE NOT BEEN REGISTERED
UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE "SECURITIES ACT"), AND MAY NOT
BE SOLD, TRANSFERRED, OR ASSIGNED UNLESS THERE IS AN EFFECTIVE REGISTRATION
STATEMENT UNDER SUCH ACT COVERING SUCH SECURITIES, THE SALE IS MADE IN
ACCORDANCE WITH RULE 144 UNDER THE SECURITIES ACT, OR THE COMPANY RECEIVES AN
OPINION OF COUNSEL FOR THE HOLDER OF SUCH SECURITIES REASONABLY SATISFACTORY TO
THE COMPANY STATING THAT SUCH SALE, TRANSFER, ASSIGNMENT OR HYPOTHECATION IS
EXEMPT FROM THE REGISTRATION AND PROSPECTUS DELIVERY REQUIREMENTS OF SUCH ACT.

THE SALE OR TRANSFER AND CERTAIN OTHER RIGHTS RELATING TO THE SECURITIES
REPRESENTED BY THIS DOCUMENT ARE SUBJECT TO THE TERMS AND CONDITIONS OF A
CERTAIN SHAREHOLDER AGREEMENT BY AND AMONG THE COMPANY AND CERTAIN SHAREHOLDERS
OF THE COMPANY. A COPY OF SUCH AGREEMENT IS ON FILE AT THE PRINCIPAL OFFICE OF
THE COMPANY.

No.: ______

                                     WARRANT
                       TO PURCHASE CLASS E PREFERRED STOCK
                                       OF
                            BEACON POWER CORPORATION

                           (void after April 7, 2005)

         1. ISSUANCE OF WARRANT. FOR VALUE RECEIVED, on and after the date of
issuance of this Warrant, and subject to the terms and conditions herein set
forth, the Holder (as defined below) is entitled to purchase from Beacon
Power Corporation, a Delaware corporation (the "Company"), at any time before
5:00 p.m. New York time on April 7, 2005 (the "Termination Date"), at a price
per share equal to $2.50 (the "Warrant Price") (subject to adjustment as
described below), ________ shares of the Class E Preferred Stock, $.01 par
value per share (the "Warrant Stock") upon exercise of this warrant (this
"Warrant") pursuant to Section 6 hereof. This Warrant is issued pursuant to
the Securities Purchase Agreement (as defined below).

         2. DEFINITIONS. As used in this Warrant, the following terms have the
definitions ascribed to them below:

                  (a) "Additional Stock" is defined in Section 3(d)(iv).

                  (b) "Business Day" means any day other than a Saturday, Sunday
or other day on which the national or state banks located in the State of
Massachusetts or the State of New York or the District of Columbia are
authorized to be closed.

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                  (c) "Change-In-Control Event" means the occurrence after the
Commencement Date of any of the following: (i) the acquisition of voting
securities of the Company by any person or group of persons that results in such
person or group, together with its affiliates, becoming, directly or indirectly,
the beneficial owner of in excess of 50% of the outstanding voting securities of
the Company; (ii) a merger or consolidation of the Company with any other
corporation or legal entity regardless of which entity is the survivor, other
than a merger or consolidation which would result in the voting securities of
the Company outstanding immediately prior thereto continuing to represent
(either by remaining outstanding or being converted into voting securities of
the surviving entity) in excess of 50% of the voting securities of the Company
or such surviving entity outstanding immediately after such merger or
consolidation; or (iii) the sale or disposition of all or substantially all of
the Company's assets other than in a transaction in which holders of the voting
securities of the Company immediately prior to such transaction receive voting
securities of the acquiror of such assets or its affiliate that represent in
excess of 50% of the voting securities of such entity after consummation of such
transaction.

                  (d) "Commencement Date" means the date of issue of this
Warrant.

                  (e) "Common Stock" means the Company's Common Stock, $.01 par
value per share.

                  (f) "Holder" means ________________ or its assigns.

                  (g) "Securities Purchase Agreement" means the Securities
Purchase Agreement dated as of April 7, 2000 by and among the Company, Perseus
Capital, L.L.C., Duquesne Enterprises, Inc., Micro Generation Technology Fund,
L.L.C., and SatCon Technology Corporation (collectively, the "Purchasers").

                  (h) "Class E Preferred Stock" means the Class E Preferred
Stock, $.01 par value per share of the Company.

         3. ADJUSTMENTS AND NOTICES. The Warrant Price and/or the number of
shares of Warrant Stock shall be subject to adjustment from time to time in
accordance with this Section 3. The Warrant Price and/or the number of Warrant
Shares shall be adjusted to reflect all of the following events that occur on or
after the Commencement Date.

                  (a) SUBDIVISION, STOCK DIVIDENDS OR COMBINATIONS. In case the
Company shall at any time subdivide the outstanding shares of Warrant Stock or
shall issue a stock dividend with respect to the Warrant Stock, the Warrant
Price in effect immediately prior to such subdivision or the issuance of such
dividend shall be proportionately decreased, and in case the Company shall at
any time combine the outstanding shares of the Warrant Stock, the Warrant Price
in effect immediately prior to such combination shall be proportionately
increased, in each case effective at the close of business on the date of such
subdivision, dividend or combination, as the case may be.

                  (b) RECLASSIFICATION, EXCHANGE, SUBSTITUTION, IN-KIND
DISTRIBUTION. Upon any

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reclassifications, exchange, substitution or other event that results in a
change of the number and/or class of the securities issuable upon exercise or
conversion of this Warrant or upon the payment of a dividend in securities or
property other than shares of Warrant Stock, the Holder shall be entitled to
receive, upon exercise or conversion of this Warrant, the number and kind of
securities and property that Holder would have received if this Warrant had been
exercised or converted immediately before the record date for such
reclassification, exchange, substitution, or other event or immediately prior to
the record date for such dividend. The Company or its successor shall promptly
issue to Holder a new warrant for such new securities or other property. The new
warrant shall provide for adjustments which shall be as nearly equivalent as may
be practicable to the adjustments provided for in this Section 3 including,
without limitation, adjustments to the Warrant Price and to the number of
securities or property issuable upon exercise or conversion of the new warrant.
The provisions of this Section 3(b) shall similarly apply to successive
reclassifications, exchanges, substitutions, or other events and successive
dividends.

                  (c) REORGANIZATION, MERGER ETC. In case of any
Change-In-Control Event, the Company, or such successor or purchasing
corporation, as the case may be, shall, as a condition to closing any such
reorganization, merger or sale, duly execute and deliver to the Holder hereof a
new warrant so that the Holder shall have the right to receive, at a total
purchase price not to exceed that payable upon the exercise or conversion of the
unexercised or unconverted portion of this Warrant, and in lieu of the shares of
the Warrant Stock theretofore issuable upon exercise or conversion of this
Warrant, the kind and amount of shares of stock, other securities, money and
property receivable upon such reorganization, merger or sale by the Holder of
the number of shares of Warrant Stock then purchasable under this Warrant. Such
new warrant shall provide for adjustments that shall be as nearly equivalent as
may be practicable to the adjustments provided for in this Section 3. The
provisions of this subparagraph (c) shall similarly apply to successive
Change-In-Control Events.

                  (d) DILUTIVE ISSUANCES ADJUSTMENT OF NUMBER OF SHARES AND
WARRANT PRICE. In order to prevent dilution of the rights granted under this
Warrant, the number of shares of Warrant Stock obtainable upon exercise of this
Warrant and the Warrant Price shall be subject to adjustment from time to time
as provided in this Section 3(d).

                           (i) ADJUSTMENT OF WARRANT PRICE UPON ISSUANCE OF
ADDITIONAL STOCK. If and whenever after the Commencement Date, the Company
issues, or in accordance with Section 3(d)(ii) is deemed to have issued, any
Additional Stock to any person for a consideration per share less than the
Warrant Price then in effect, then the Warrant Price in effect immediately
before each such issuance shall forthwith be adjusted to a price determined by
multiplying such Warrant Price by a fraction, the NUMERATOR of which shall be
the number of shares of Common Stock outstanding immediately prior to such
issuance plus the number of shares of Common Stock that the aggregate
consideration received by the Company for such issuance would purchase at such
Warrant Price; and the DENOMINATOR of which shall be the number of shares of
Common Stock outstanding immediately prior to such issuance plus the number of
shares of such Additional Stock.

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                           (ii) EFFECT OF CERTAIN EVENTS. For purposes of
determining under Section (d)(i) the adjusted number of shares of Warrant Stock
acquirable upon exercise of this Warrant, the following shall be applicable:

                                        (A) ISSUANCE OF RIGHTS OR OPTIONS. If
                    the Company in any manner issues, grants or sells (or
                    otherwise becomes subject to) any options, rights, or
                    warrants (collectively, "Options") to purchase Common Stock
                    or securities that are convertible into or exchangeable for
                    Common Stock ("Convertible Securities"), then the total
                    maximum number of shares of Common Stock issuable upon the
                    exercise of such Options or upon conversion or exchange of
                    the total maximum amount of such Convertible Securities
                    issuable upon the exercise of such Options shall be deemed
                    to have been sold on the date of issuance, grant or sale of
                    such Options and to be outstanding, and the total maximum
                    consideration receivable for such issue, grant and sale of
                    the Options, Convertible Securities and Common Stock shall
                    be deemed to have been received by the Company.

                                        (B) ISSUANCE OF CONVERTIBLE SECURITIES.
                    If the Company in any manner grants, issues or sells (or
                    otherwise becomes subject to) any Convertible Securities,
                    then the maximum number of shares of Common Stock issuable
                    upon conversion or exchange of such Convertible Securities
                    shall be deemed to have been sold on the date of issuance,
                    grant or sale of such Convertible Securities and to be
                    outstanding, and the total maximum consideration receivable
                    for such grant, issue and sale of the Convertible Securities
                    and Common Stock shall be deemed to have been received by
                    the Company.

                                        (C) TREATMENT OF EXPIRED OPTIONS AND
                    UNEXERCISED CONVERTIBLE SECURITIES. Upon the expiration of
                    any Option or the termination of any right to convert or
                    exchange any Convertible Securities without the exercise of
                    such Option or right, the number of shares of Warrant Stock
                    acquirable hereunder shall be adjusted to the number of
                    shares which would have been in effect at the time of such
                    expiration or termination had such Option or Convertible
                    Securities, to the extent outstanding immediately prior to
                    such expiration or termination, never been issued and the
                    consideration for such exercise never been received.

                                        (D) TREASURY SHARES. The number of
                    shares of Common Stock outstanding at any given time does
                    not include shares owned or held by or for the account of
                    the Company or any Subsidiary, and the disposition of any
                    shares so owned or held shall be considered an issuance or
                    sale of Common Stock.

                                        (E) RECORD DATE. If the Company takes a
                    record of the holders of Common Stock for the purpose of
                    entitling them (A) to receive a dividend or other
                    distribution payable in Common Stock, Options or in
                    Convertible Securities or (B) to subscribe for or purchase
                    Common Stock, Options or Convertible Securities, then such
                    record date shall be deemed to be the date of the issue or
                    sale of the shares of Common Stock deemed to have been
                    issued or sold upon the declaration of such dividend or the

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                    making of such other distribution or the date of the
                    granting of such right of subscription or purchase, as the
                    case may be.

                           (iii) In the case of the issuance of Additional Stock
for cash, the consideration received therefor shall be deemed to be the
amount of cash paid therefor before deducting any reasonable discounts,
commissions or other expenses allowed, paid or incurred by the company for any
underwriting or otherwise in connection with the issuance and sale thereof. In
the case of the issuance of Additional Stock for a consideration in whole or in
part other than cash, the consideration other than cash received therefor shall
be deemed to be the fair value thereof as reasonably determined by the Board of
Directors of the Company in its good faith judgment irrespective of any
accounting treatment.

                           (iv) "Additional Stock" shall mean any shares of
Common Stock issued (or deemed to have been issued pursuant to clause (ii) of
this Section 3(d)) by the Company after the Commencement Date, other than shares
of Common Stock issued or issuable:

                                        (A) to officers, directors, employees
                    and consultants of the Company directly or pursuant to a
                    stock option plan or restricted stock plan approved by the
                    Board of Directors of the Company; or

                                        (B) upon conversion of the Class A, B,
                    C, D or E Preferred Stock of the Company or the exercise of
                    warrants issued by the Company before or on the Commencement
                    Date.

                           (v) CERTAIN EVENTS. If any event occurs of the type
contemplated by the provisions of this Section 3(d) but not expressly
provided for by such provisions (including, without limitation, the granting of
stock appreciation rights, phantom stock rights or other rights with equity
features), then the Company's board of directors shall make an appropriate
adjustment in the number of shares of Warrant Stock obtainable upon exercise of
this Warrant and in the Warrant Price so as to protect the rights of the holders
of the Warrants; provided that no such adjustment shall decrease the number of
shares of Warrant Stock obtainable as otherwise determined pursuant to this
Section 3.

                  (e) CERTIFICATE OF ADJUSTMENT. In each case of an adjustment
or readjustment of the Warrant Price, the Corporation, at its own expense, shall
cause its Chief Financial Officer to compute such adjustment or readjustment in
accordance with the provisions hereof and prepare a certificate showing such
adjustment or readjustment, and shall mail such certificate, by first class
mail, postage prepaid, to the Holder. The certificate shall set forth such
adjustment or readjustment, showing in detail the facts upon which such
adjustment or readjustment is based. No adjustment of the Warrant Price shall be
required to be made unless it would result in an increase or decrease of at
least one cent, but any adjustments not made because of this sentence shall be
carried forward and taken into account in any subsequent adjustment otherwise
required hereunder.

                  (f) NO IMPAIRMENT. The Company shall not, by amendment of its
Certificate

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of Incorporation or through a reorganization, transfer of assets, consolidation,
merger, dissolution, issue, or sale of securities or any other voluntary action,
avoid or seek to avoid the observance or performance of any of the terms to be
observed or performed under this Warrant by the Company, but shall at all times
in good faith assist in carrying out all of the provisions of this Section 3 and
in taking all such action as may be necessary or appropriate to protect the
Holder's rights under this Section 3 against impairment. If the Company takes
any action affecting the Class E Preferred Stock other than as described above
that adversely affects the Holder's rights under this Warrant, the Warrant Price
shall be adjusted downward.

                  (g) FRACTIONAL SHARES. No fractional shares shall be issuable
upon exercise or conversion of the Warrant and the number of shares to be issued
shall be rounded down to the nearest whole share. If a fractional share interest
arises upon any exercise or conversion of the Warrant, the Company shall
eliminate such fractional share interest by paying the Holder an amount computed
by multiplying the fractional interest by the fair market value of a full share.

         4. NO SHAREHOLDER RIGHTS. This Warrant, by itself, as distinguished
from any shares purchased hereunder, shall not entitle its Holder to any of the
rights of a shareholder of the Company.

         5. RESERVATION OF STOCK. On and after the Warrant Stock Definition
Date, the Company will reserve from its authorized and unissued stock a
sufficient number of shares to provide for the issuance of Warrant Stock upon
the exercise or conversion of this Warrant. Issuance of this Warrant shall
constitute full authority to the Company's officers who are charged with the
duty of executing stock certificates to execute and issue the necessary
certificates for shares of Warrant Stock issuable upon the exercise or
conversion of this Warrant.

         6. EXERCISE OF WARRANT. This Warrant may be exercised as a whole or in
part by the Holder, at any time after the date hereof prior to the termination
of this Warrant, by the surrender of this Warrant, together with the Notice of
Exercise and Investment Representation Statement in the forms attached hereto as
ATTACHMENTS 1 AND 2, respectively, duly completed and executed at the principal
office of the Company, specifying the portion of the Warrant to be exercised and
accompanied by payment in full of the Warrant Price in cash or by check with
respect to the shares of Warrant Stock being purchased. This Warrant shall be
deemed to have been exercised immediately prior to the close of business on the
date of its surrender for exercise as provided above, and the person entitled to
receive the shares of Warrant Stock issuable upon such exercise shall be treated
for all purposes as the holder of such shares of record as of the close of
business on such date. As promptly as practicable after such date, the Company
shall issue and deliver to the person or persons entitled to receive the same a
certificate or certificates for the number of full shares of Warrant Stock
issuable upon such exercise. If this Warrant shall be exercised for less than
the total number of shares of Warrant Stock then issuable upon exercise,
promptly after surrender of this Warrant upon such exercise, the Company will
execute and deliver a new warrant, dated the date hereof, evidencing the right
of the Holder to the balance of this Warrant Stock purchasable hereunder upon
the same terms and conditions set forth herein.

         7. CONVERSION. In lieu of exercising this Warrant or any portion
hereof, at any time

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after the occurrence of a Change-In-Control Event or the filing of a
registration statement for an initial underwritten public offering of securities
by the Company, the Holder hereof shall have the right to convert this Warrant
or any portion hereof into Warrant Stock by executing and delivering to the
Company at its principal office the written Notice of Conversion and Investment
Representation Statement in the forms attached hereto as ATTACHMENTS 2 AND 3,
specifying the portion of the Warrant to be converted, and accompanied by this
Warrant. The number of shares of Warrant Stock to be issued to Holder upon such
conversion shall be computed using the following formula:

                                 X=(P)(Y)(A-B)/A

         where X =         the number of shares of Warrant Stock to be issued to
                           the Holder for the portion of the Warrant being
                           converted.

                           P =      the portion of the Warrant being converted
                                    expressed as a decimal fraction.

                           Y =      the total number of shares of Warrant Stock
                                    issuable upon exercise of the Warrant in
                                    full.

                           A =      the fair market value of one share of
                                    Warrant Stock which means (i) the fair
                                    market value of the Warrant Stock as of the
                                    last Business Day immediately prior to the
                                    date the notice of conversion is received by
                                    the Company, as reported in the principal
                                    market for such securities or, if no such
                                    market exists, as determined in good faith
                                    by the Company's Board of Directors, or (ii)
                                    if this Warrant is being converted in
                                    conjunction with a public offering of stock
                                    the price to the public per share pursuant
                                    to the offering.

                           B =      the Warrant Price on the date of conversion.

Any portion of this Warrant that is converted shall be immediately canceled.
This Warrant or any portion hereof shall be deemed to have been converted
immediately prior to the close of business on the date of its surrender for
conversion as provided above, and the person entitled to receive the shares of
Warrant Stock issuable upon such conversion shall be treated for all purposes as
the holder of such shares of record as of the close of business on such date. As
promptly as practicable after such date, the Company shall issue and deliver to
the person or persons entitled to receive the same a certificate or certificates
for the number of full shares of Warrant Stock issuable upon such conversion. If
the Warrant shall be converted for less than the total number of shares of
Warrant Stock then issuable upon conversion, promptly after surrender of the
Warrant upon such conversion, the Company will execute and deliver a new
warrant, dated the date hereof, evidencing the right of the Holder to the
balance of the Warrant Stock purchasable hereunder upon the same terms and
conditions set forth herein. If this Warrant is

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converted, as a whole or in part, after the occurrence of a Change-In-Control
Event as to which Section 3(c) is applicable, the Holder shall receive the
consideration contemplated by Section 3(c) in lieu of Warrants Stock of the
Company.

         8. TRANSFER OF WARRANT. This Warrant may be transferred or assigned by
the Holder hereof as a whole or in part, provided that the transferor provides,
at the Company's request, an opinion of counsel satisfactory to the Company that
such transfer does not require registration under the Securities Act and the
securities law applicable with respect to any other applicable jurisdiction.

         9. TERMINATION. This Warrant shall terminate on 5:00 p.m. New York time
on the Termination Date.

         10. MISCELLANEOUS. This Warrant shall be governed by the laws of the
Commonwealth of Massachusetts, as such laws are applied to contracts to be
entered into and performed entirely in Massachusetts by Massachusetts residents.
In the event of any dispute among the Holder and the Company arising out of the
terms of this Warrant, the parties hereby consent to the exclusive jurisdiction
of the federal and state courts located in the Commonwealth of Massachusetts for
resolution of such dispute, and agree not to contest such exclusive jurisdiction
or seek to transfer any action relating to such dispute to any other
jurisdiction. The headings in this Warrant are for purposes of convenience and
reference only, and shall not be deemed to constitute a part hereof. Neither
this Warrant nor any term hereof may be changed or waived orally, but only by an
instrument in writing signed by the Company and the Holder of this Warrant. All
notices and other communications from the Company to the Holder of this Warrant
shall be delivered personally or by facsimile transmission or mailed by first
class mail, postage prepaid, to the address or facsimile number furnished to the
Company in writing by the last Holder of this Warrant who shall have furnished
an address or facsimile number to the Company in writing, and if mailed shall be
deemed given three days after deposit in the United States mail.

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         ISSUED:  April 7, 2000

                  BEACON POWER CORPORATION

                  By:__________________________________

                  Name:    William E. Stanton

                  Title:   President

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<PAGE>

                                  Attachment 1

NOTICE OF EXERCISE

TO:      BEACON POWER CORPORATION

1.   The undersigned hereby elects to purchase _______________ shares of the
     Warrant Stock of Beacon Power Corporation pursuant to the terms of the
     attached Warrant, and tenders herewith payment of the purchase price in
     full, together with all applicable transfer taxes, if any.

2.   Please issue a certificate or certificates representing said shares of
     Warrant Stock in the name of the undersigned or in such other name as is
     specified below:

                         ------------------------------
                                     (Name)

                         -------------------------------
                                    (Address)

---------------------------------------     -----------------------------------
(Date)   (Name of Warrant Holder)

     By:_______________________________

     Title:____________________________

<PAGE>

                                  Attachment 2

                       INVESTMENT REPRESENTATION STATEMENT

                      Shares of the Class E Preferred Stock
                     (as defined in the attached Warrant) of
                            BEACON POWER CORPORATION

         In connection with the purchase of the above-listed securities, the
undersigned hereby represents to Beacon Power Corporation (the "Company") as
follows:

(a) The securities to be received upon the exercise of the Warrant (the
"Securities") will be acquired for investment for its own account, not as a
nominee or agent, and not with a view to the sale or distribution of any part
thereof, and the undersigned has no present intention of selling, granting
participation in or otherwise distributing the same, but subject, nevertheless,
to any requirement of law that the disposition of its property shall at all
times be within its control. By executing this statement, the undersigned
further represents that it does not have any contract, undertaking, agreement or
arrangement with any person to sell, transfer, or grant participations to such
person or to any third person, with respect to any Securities issuable upon
exercise of the Warrant.

(b) The undersigned understands that the Securities issuable upon exercise of
the Warrant at the time of issuance may not be registered under the Securities
Act of 1933, as amended (the "Securities Act"), and applicable state securities
laws, on the ground that the issuance of such securities is exempt pursuant to
Section 4(2) of the Securities Act and state law exemptions relating to offers
and sales not by means of a public offering, and that the Company's reliance on
such exemptions is predicated on the undersigned's representations set forth
herein.

(c) The undersigned agrees that in no event will it make a disposition of any
Securities acquired upon the exercise of the Warrant unless and until (i) it
shall have notified the Company of the proposed disposition and shall have
furnished the Company with a statement of the circumstances surrounding the
proposed disposition, and (ii) it shall have furnished the Company with an
opinion of counsel satisfactory to the Company and Company's counsel to the
effect that (A) appropriate action necessary for compliance with the Securities
Act and any applicable state securities laws has been taken or an exemption from
the registration requirements of the Securities Act and such laws is available,
and (B) the proposed transfer will not violate any of said laws.

(d) The undersigned acknowledges that an investment in the Company is highly
speculative and represents that it is able to fend for itself in the
transactions contemplated by this statement, has such knowledge and experience
in financial and business matters as to be capable of evaluating the merits and
risks of its investments, and has the ability to bear the economic risks
(including the risk of a total loss) of its investment. The undersigned
represents that it has had the opportunity to ask questions of the Company
concerning the Company's business and assets and to obtain any additional
information which it considered necessary to verify the accuracy of or to

<PAGE>

amplify the Company's disclosures, and has had all questions which have been
asked by it satisfactorily answered by the Company

(e) The undersigned acknowledges that the Securities issuable upon exercise or
conversion of the Warrant must be held indefinitely unless subsequently
registered under the Securities Act or an exemption from such registration is
available. The undersigned is aware of the provisions of Rule 144 promulgated
under the Securities Act which permit limited resale of shares purchased in a
private placement subject to the satisfaction of certain conditions, including,
among other things, the existence of a public market for the shares, the
availability of certain current public information about the Company, the resale
occurring not less than one year after a party has purchased and paid for the
security to be sold from the Company or any affiliate of the Company, the sale
being through a "broker's transaction" or in transactions directly with a
"market maker" (as provided by Rule 144(f)) and the number of shares being sold
during any three month period not exceeding specified limitations.

         Dated:________________________

         _______________________________________
         (Typed or Printed Name)

         By:____________________________________
              (Signature)

         _______________________________________
         (Title)

<PAGE>

                                  Attachment 3

NOTICE OF CONVERSION

TO:      BEACON POWER CORPORATION

1. The undersigned hereby elects to acquire _______________ shares of the
Warrant Stock of Beacon Power Corporation pursuant to the terms of the attached
Warrant, by conversion of _________ percent (_____%) of the Warrant.

2. Please issue a certificate or certificates representing said shares of
Warrant Stock in the name of the undersigned or in such other name as is
specified below:

                         ------------------------------
                                     (Name)

                         -------------------------------
                                    (Address)

---------------------------------------     -----------------------------------
(Date)   (Name of Warrant Holder)

  By:________________________________

  Title:_______________________________
    (Title and signature of authorized person)

<PAGE>

         FIRST AMENDMENT TO WARRANT TO PURCHASE CLASS E PREFERED STOCK

                           OF BEACON POWER CORPORATION

       This First Amendment to Warrant to Purchase Class E Preferred Stock of
Beacon Power Corporation (this "AMENDMENT") is entered into this July 24, 2000
by and between Beacon Power Corporation (the "COMPANY"), and
____________________, or its registered assigns (the "HOLDER").

       WHEREAS, the Company issued the Holder a certain Warrant to Purchase
Class E Preferred Stock of Beacon Power Corporation dated April 7, 2000 (the
"WARRANT"); and --------

       WHEREAS, the Company and the Holder are desirous of amending the Warrant
in the manner set forth below;

       NOW THEREFORE, for good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the Company and the Holder agree
as follows:

       1. The Warrant is hereby amended, by deleting Section 3(b) and replacing
it with the following:

                (b) RECLASSIFICATION, EXCHANGE, SUBSTITUTION, IN-KIND
                DISTRIBUTION. Upon any reclassifications, exchange, substitution
                or other event that results in a change of the number and/or
                class of the securities issuable upon exercise or conversion of
                this Warrant or upon the payment of a dividend in securities or
                property other than shares of Warrant Stock, the Holder shall be
                entitled to receive, upon exercise or conversion of this
                Warrant, the number and kind of securities and property that
                Holder would have received if this Warrant had been exercised or
                converted immediately before the record date for such
                reclassification, exchange, substitution, or other event or
                immediately prior to the record date for such dividend. The
                Company or its successor shall promptly issue to Holder a new
                warrant for such new securities or other property. The new
                warrant shall provide for adjustments which shall be as nearly
                equivalent as may be practicable to the adjustments provided for
                in this Section 3 including, without limitation, adjustments to
                the Warrant Price and to the number of securities or property
                issuable upon exercise or conversion of the new warrant. Without
                any further action by the Holder or the Company, in the event
                the Company's issued and outstanding Class E Preferred Stock is
                converted into another class or series of the Company's capital
                securities, the Warrant Stock issuable pursuant to this Warrant
                shall likewise be deemed to be automatically converted into the
                same class or series and on the same terms that the issued and
                outstanding Class E Preferred Stock was converted. The
                provisions of this Section 3(b) shall similarly apply to
                successive reclassifications, exchanges, substitutions, or other
                events and successive dividends.

       2. Except as specifically provided herein, all terms and conditions of
the Warrant shall remain in full force and effect and are hereby ratified and
confirmed. On and after the date hereof, each reference in the Warrant to "this
Warrant", "hereunder", "hereof" or words of like import referring to the
Warrant, shall mean and be a reference to the Warrant as amended by this
Amendment.

       This Amendment shall take effect as a sealed instrument under the laws of
the Commonwealth of Massachusetts as of the date first written above.

                                   BEACON POWER CORPORATION

                                   By:
                                      ------------------------------------

                                   Title:
                                         ---------------------------------

                                   ------------------------------------

                                   By:
                                      ------------------------------------
                                   Title:                                \
                                         ---------------------------------

<PAGE>

                      WARRANTS OF BEACON POWER CORPORATION

                      ISSUED PURSUANT TO CLASS E FINANCING

<TABLE>
<CAPTION>
------------------------------------------------------------ ---------------------------------------------------------
                      Name of Holder                           Number of shares of common stock underlying warrant

------------------------------------------------------------ ---------------------------------------------------------
<S>                                                          <C>
Perseus Capital, L.L.C.                                                              688,150
------------------------------------------------------------ ---------------------------------------------------------
SatCon Technology Corporation                                                        434,259
------------------------------------------------------------ ---------------------------------------------------------
Duquesne Enterprises, Inc.                                                           255,996
------------------------------------------------------------ ---------------------------------------------------------
Micro-Generation Technology Fund, L.L.C.                                             154,271
------------------------------------------------------------ ---------------------------------------------------------
</TABLE><PAGE>

                                                                 Exhibit 10.1.9

THE SECURITIES EVIDENCED BY THIS WARRANT CERTIFICATE HAVE NOT BEEN REGISTERED
UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE "SECURITIES ACT"), AND MAY NOT
BE SOLD, TRANSFERRED, OR ASSIGNED UNLESS THERE IS AN EFFECTIVE REGISTRATION
STATEMENT UNDER SUCH ACT COVERING SUCH SECURITIES, THE SALE IS MADE IN
ACCORDANCE WITH RULE 144 UNDER THE SECURITIES ACT, OR THE COMPANY RECEIVES AN
OPINION OF COUNSEL FOR THE HOLDER OF SUCH SECURITIES REASONABLY SATISFACTORY TO
THE COMPANY STATING THAT SUCH SALE, TRANSFER, ASSIGNMENT OR HYPOTHECATION IS
EXEMPT FROM THE REGISTRATION AND PROSPECTUS DELIVERY REQUIREMENTS OF SUCH ACT.

THE SALE OR TRANSFER AND CERTAIN OTHER RIGHTS RELATING TO THE SECURITIES
REPRESENTED BY THIS DOCUMENT ARE SUBJECT TO THE TERMS AND CONDITIONS OF A
CERTAIN SHAREHOLDER AGREEMENT BY AND AMONG THE COMPANY AND CERTAIN SHAREHOLDERS
OF THE COMPANY. A COPY OF SUCH AGREEMENT IS ON FILE AT THE PRINCIPAL OFFICE OF
THE COMPANY.

No.: ____

                                     WARRANT

                            TO PURCHASE COMMON STOCK

                                       OF

                            BEACON POWER CORPORATION

                           (void after April 21, 2005)

         1. ISSUANCE OF WARRANT. FOR VALUE RECEIVED, on and after the date of
issuance of this Warrant, and subject to the terms and conditions herein set
forth, the Holder (as defined below) is entitled to purchase from Beacon Power
Corporation, a Delaware corporation (the "Company"), at any time before 5:00
p.m. New York time on April 21, 2005 (the "Termination Date"), at a price per
share equal to $4.20 (the "Warrant Price") (subject to adjustment as described
below), ____ shares of the Common Stock, $.01 par value per share (the "Warrant
Stock") upon exercise of this warrant (this "Warrant") pursuant to Section 6
hereof. This Warrant is issued pursuant to the Securities Purchase Agreement (as
defined below).

         2. DEFINITIONS. As used in this Warrant, the following terms have the
definitions ascribed to them below:

                  (a) "Additional Stock" is defined in Section 3(d)(iv).

                  (b) "Business Day" means any day other than a Saturday, Sunday
or other day on which the national or state banks located in the State of
Massachusetts or the State of New York or the District of Columbia are
authorized to be closed.

<PAGE>

                  (c) "Change-In-Control Event" means the occurrence after the
Commencement Date of any of the following: (i) the acquisition of voting
securities of the Company by any person or group of persons that results in such
person or group, together with its affiliates, becoming, directly or indirectly,
the beneficial owner of in excess of 50% of the outstanding voting securities of
the Company; (ii) a merger or consolidation of the Company with any other
corporation or legal entity regardless of which entity is the survivor, other
than a merger or consolidation which would result in the voting securities of
the Company outstanding immediately prior thereto continuing to represent
(either by remaining outstanding or being converted into voting securities of
the surviving entity) in excess of 50% of the voting securities of the Company
or such surviving entity outstanding immediately after such merger or
consolidation; or (iii) the sale or disposition of all or substantially all of
the Company's assets other than in a transaction in which holders of the voting
securities of the Company immediately prior to such transaction receive voting
securities of the acquiror of such assets or its affiliate that represent in
excess of 50% of the voting securities of such entity after consummation of such
transaction.

                  (d) "Commencement Date" means the date of issue of this
Warrant.

                  (e) "Common Stock" means the Company's Common Stock, $.01 par
value per share.

                  (f) "Holder" means _____________, or its assigns.

                  (g) "Note and Warrant Purchase Agreement" means the Note and
Warrant Purchase Agreement dated as of April 21, 2000 by and among the Company
and the Purchasers named therein and signatory thereto.

                  (h) "Class F Preferred Stock" means the Class F Preferred
Stock, $.01 par value per share, of the Company.

         3. ADJUSTMENTS AND NOTICES. The Warrant Price and/or the number of
shares of Warrant Stock shall be subject to adjustment from time to time in
accordance with this Section 3. The Warrant Price and/or the number of Warrant
Shares shall be adjusted to reflect all of the following events that occur on or
after the Commencement Date.

                  (a) SUBDIVISION, STOCK DIVIDENDS OR COMBINATIONS. In case the
Company shall at any time subdivide the outstanding shares of Warrant Stock or
shall issue a stock dividend with respect to the Warrant Stock, the Warrant
Price in effect immediately prior to such subdivision or the issuance of such
dividend shall be proportionately decreased, and in case the Company shall at
any time combine the outstanding shares of the Warrant Stock, the Warrant Price
in effect immediately prior to such combination shall be proportionately
increased, in each case effective at the close of business on the date of such
subdivision, dividend or combination, as the case may be.

                  (b) RECLASSIFICATION, EXCHANGE, SUBSTITUTION, IN-KIND
DISTRIBUTION. Upon any reclassifications, exchange, substitution or other event
that results in a change of the number

                                      -2-
<PAGE>

and/or class of the securities issuable upon exercise or conversion of this
Warrant or upon the payment of a dividend in securities or property other than
shares of Warrant Stock, the Holder shall be entitled to receive, upon exercise
or conversion of this Warrant, the number and kind of securities and property
that Holder would have received if this Warrant had been exercised or converted
immediately before the record date for such reclassification, exchange,
substitution, or other event or immediately prior to the record date for such
dividend. The Company or its successor shall promptly issue to Holder a new
warrant for such new securities or other property. The new warrant shall provide
for adjustments which shall be as nearly equivalent as may be practicable to the
adjustments provided for in this Section 3 including, without limitation,
adjustments to the Warrant Price and to the number of securities or property
issuable upon exercise or conversion of the new warrant. The provisions of this
Section 3(b) shall similarly apply to successive reclassifications, exchanges,
substitutions, or other events and successive dividends.

                  (c) REORGANIZATION, MERGER ETC. In case of any
Change-In-Control Event, the Company, or such successor or purchasing
corporation, as the case may be, shall, as a condition to closing any such
reorganization, merger or sale, duly execute and deliver to the Holder hereof a
new warrant so that the Holder shall have the right to receive, at a total
purchase price not to exceed that payable upon the exercise or conversion of the
unexercised or unconverted portion of this Warrant, and in lieu of the shares of
the Warrant Stock theretofore issuable upon exercise or conversion of this
Warrant, the kind and amount of shares of stock, other securities, money and
property receivable upon such reorganization, merger or sale by the Holder of
the number of shares of Warrant Stock then purchasable under this Warrant. Such
new warrant shall provide for adjustments that shall be as nearly equivalent as
may be practicable to the adjustments provided for in this Section 3. The
provisions of this subparagraph (c) shall similarly apply to successive
Change-In-Control Events.

                  (d) DILUTIVE ISSUANCES ADJUSTMENT OF NUMBER OF SHARES AND
WARRANT PRICE. In order to prevent dilution of the rights granted under this
Warrant, the number of shares of Warrant Stock obtainable upon exercise of this
Warrant and the Warrant Price shall be subject to adjustment from time to time
as provided in this Section 3(d).

         (i) ADJUSTMENT OF WARRANT PRICE UPON ISSUANCE OF ADDITIONAL STOCK. If
and whenever after the Commencement Date, the Company issues, or in accordance
with Section 3(d)(ii) is deemed to have issued, any Additional Stock to any
person for a consideration per share less than the Warrant Price then in effect,
then the Warrant Price in effect immediately before each such issuance shall
forthwith be adjusted to a price determined by multiplying such Warrant Price by
a fraction, the NUMERATOR of which shall be the number of shares of Common Stock
outstanding immediately prior to such issuance plus the number of shares of
Common Stock that the aggregate consideration received by the Company for such
issuance would purchase at such Warrant Price; and the DENOMINATOR of which
shall be the number of shares of Common Stock outstanding immediately prior to
such issuance plus the number of shares of such Additional Stock. In addition,
upon each adjustment of the Exercise Price under this Section 3, the number of
Warrant Shares acquirable upon the exercise of this Warrant shall be adjusted to
equal the number of shares determined by multiplying the Exercise Price in
effect immediately prior to the

                                      -3-
<PAGE>

adjustment of the Warrant Price by the number of Warrant Shares acquirable upon
exercise of this Warrant immediately prior to the adjustment of the Warrant
Price and dividing the product thereof by the Exercise Price resulting from the
adjustment of the Warrant Price.

                           (ii) EFFECT OF CERTAIN EVENTS. For purposes of
determining under Section (d)(i) the adjusted number of shares of Warrant Stock
acquirable upon exercise of this Warrant, the following shall be applicable:

                                        (A) ISSUANCE OF RIGHTS OR OPTIONS. If
                    the Company in any manner issues, grants or sells (or
                    otherwise becomes subject to) any options, rights, or
                    warrants (collectively, "Options") to purchase Common Stock
                    or securities that are convertible into or exchangeable for
                    Common Stock ("Convertible Securities"), then the total
                    maximum number of shares of Common Stock issuable upon the
                    exercise of such Options or upon conversion or exchange of
                    the total maximum amount of such Convertible Securities
                    issuable upon the exercise of such Options shall be deemed
                    to have been sold on the date of issuance, grant or sale of
                    such Options and to be outstanding, and the total maximum
                    consideration receivable for such issue, grant and sale of
                    the Options, Convertible Securities and Common Stock shall
                    be deemed to have been received by the Company.

                                        (B) ISSUANCE OF CONVERTIBLE SECURITIES.
                    If the Company in any manner grants, issues or sells (or
                    otherwise becomes subject to) any Convertible Securities,
                    then the maximum number of shares of Common Stock issuable
                    upon conversion or exchange of such Convertible Securities
                    shall be deemed to have been sold on the date of issuance,
                    grant or sale of such Convertible Securities and to be
                    outstanding, and the total maximum consideration receivable
                    for such grant, issue and sale of the Convertible Securities
                    and Common Stock shall be deemed to have been received by
                    the Company.

                                        (C) TREATMENT OF EXPIRED OPTIONS AND
                    UNEXERCISED CONVERTIBLE SECURITIES. Upon the expiration of
                    any Option or the termination of any right to convert or
                    exchange any Convertible Securities without the exercise of
                    such Option or right, the number of shares of Warrant Stock
                    acquirable hereunder shall be adjusted to the number of
                    shares which would have been in effect at the time of such
                    expiration or termination had such Option or Convertible
                    Securities, to the extent outstanding immediately prior to
                    such expiration or termination, never been issued and the
                    consideration for such exercise never been received.

                                        (D) TREASURY SHARES. The number of
                    shares of Common Stock outstanding at any given time does
                    not include shares owned or held by or for the account of
                    the Company or any Subsidiary, and the disposition of any
                    shares so owned or held shall be considered an issuance or
                    sale of Common Stock.

                                        (E) RECORD DATE. If the Company takes a
                    record of the holders of Common Stock for the purpose of
                    entitling them (A) to receive a dividend or other

                                      -4-
<PAGE>

                    distribution payable in Common Stock, Options or in
                    Convertible Securities or (B) to subscribe for or purchase
                    Common Stock, Options or Convertible Securities, then such
                    record date shall be deemed to be the date of the issue or
                    sale of the shares of Common Stock deemed to have been
                    issued or sold upon the declaration of such dividend or the
                    making of such other distribution or the date of the
                    granting of such right of subscription or purchase, as the
                    case may be.

                           (iii) In the case of the issuance of Additional Stock
for cash, the consideration received therefor shall be deemed to be the amount
of cash paid therefor before deducting any reasonable discounts, commissions or
other expenses allowed, paid or incurred by the company for any underwriting or
otherwise in connection with the issuance and sale thereof. In the case of the
issuance of Additional Stock for a consideration in whole or in part other than
cash, the consideration other than cash received therefor shall be deemed to be
the fair value thereof as reasonably determined by the Board of Directors of the
Company in its good faith judgment irrespective of any accounting treatment.

                           (iv) "Additional Stock" shall mean any shares of
Common Stock issued (or deemed to have been issued pursuant to clause (ii) of
this Section 3(d)) by the Company after the Commencement Date, other than shares
of Common Stock issued or issuable:

                                        (A) to officers, directors, employees
                    and consultants of the Company directly or pursuant to a
                    stock option plan or restricted stock plan approved by the
                    Board of Directors of the Company; or

                                        (B) upon conversion of the Class A, B,
                    C, D or E Preferred Stock of the Company or the exercise of
                    warrants issued by the Company before or on the Commencement
                    Date.

                           (v) CERTAIN EVENTS. If any event occurs of the type
contemplated by the provisions of this Section 3(d) but not expressly
provided for by such provisions (including, without limitation, the granting of
stock appreciation rights, phantom stock rights or other rights with equity
features), then the Company's board of directors shall make an appropriate
adjustment in the number of shares of Warrant Stock obtainable upon exercise of
this Warrant and in the Warrant Price so as to protect the rights of the holders
of the Warrants; provided that no such adjustment shall decrease the number of
shares of Warrant Stock obtainable as otherwise determined pursuant to this
Section 3.

                  (e) CERTIFICATE OF ADJUSTMENT. In each case of an adjustment
or readjustment of the Warrant Price, the Corporation, at its own expense, shall
cause its Chief Financial Officer to compute such adjustment or readjustment in
accordance with the provisions hereof and prepare a certificate showing such
adjustment or readjustment, and shall mail such certificate, by first class
mail, postage prepaid, to the Holder. The certificate shall set forth such
adjustment or readjustment, showing in detail the facts upon which such
adjustment or readjustment is based. No adjustment of the Warrant Price shall be
required to be made unless it would result in an increase or decrease of at
least one cent, but any adjustments not made because of this sentence

                                      -5-
<PAGE>

shall be carried forward and taken into account in any subsequent adjustment
otherwise required hereunder.

                  (f) NO IMPAIRMENT. The Company shall not, by amendment of its
Certificate of Incorporation or through a reorganization, transfer of assets,
consolidation, merger, dissolution, issue, or sale of securities or any other
voluntary action, avoid or seek to avoid the observance or performance of any of
the terms to be observed or performed under this Warrant by the Company, but
shall at all times in good faith assist in carrying out all of the provisions of
this Section 3 and in taking all such action as may be necessary or appropriate
to protect the Holder's rights under this Section 3 against impairment. If the
Company takes any action affecting the Class F Preferred Stock other than as
described above that adversely affects the Holder's rights under this Warrant,
the Warrant Price shall be adjusted downward.

                  (g) FRACTIONAL SHARES. No fractional shares shall be issuable
upon exercise or conversion of the Warrant and the number of shares to be issued
shall be rounded down to the nearest whole share. If a fractional share interest
arises upon any exercise or conversion of the Warrant, the Company shall
eliminate such fractional share interest by paying the Holder an amount computed
by multiplying the fractional interest by the fair market value of a full share.

         4. NO SHAREHOLDER RIGHTS. This Warrant, by itself, as distinguished
from any shares purchased hereunder, shall not entitle its Holder to any of the
rights of a shareholder of the Company.

         5. RESERVATION OF STOCK. On and after the date hereof, the Company will
reserve from its authorized and unissued stock a sufficient number of shares to
provide for the issuance of Warrant Stock upon the exercise or conversion of
this Warrant. Issuance of this Warrant shall constitute full authority to the
Company's officers who are charged with the duty of executing stock certificates
to execute and issue the necessary certificates for shares of Warrant Stock
issuable upon the exercise or conversion of this Warrant.

         6. EXERCISE OF WARRANT. This Warrant may be exercised as a whole or in
part by the Holder, at any time after the date hereof prior to the termination
of this Warrant, by the surrender of this Warrant, together with the Notice of
Exercise and Investment Representation Statement in the forms attached hereto as
ATTACHMENTS 1 AND 2, respectively, duly completed and executed at the principal
office of the Company, specifying the portion of the Warrant to be exercised and
accompanied by payment in full of the Warrant Price in cash or by check with
respect to the shares of Warrant Stock being purchased. This Warrant shall be
deemed to have been exercised immediately prior to the close of business on the
date of its surrender for exercise as provided above, and the person entitled to
receive the shares of Warrant Stock issuable upon such exercise shall be treated
for all purposes as the holder of such shares of record as of the close of
business on such date. As promptly as practicable after such date, the Company
shall issue and deliver to the person or persons entitled to receive the same a
certificate or certificates for the number of full shares of Warrant Stock
issuable upon such exercise. If this Warrant shall be exercised for less than
the total number of shares of Warrant Stock then issuable upon exercise,
promptly after surrender of this Warrant upon such exercise, the Company will
execute and deliver a new

                                      -6-
<PAGE>

warrant, dated the date hereof, evidencing the right of the Holder to the
balance of this Warrant Stock purchasable hereunder upon the same terms and
conditions set forth herein.

         7. CONVERSION. In lieu of exercising this Warrant or any portion
hereof, at any time after the occurrence of a Change-In-Control Event or the
filing of a registration statement for an initial underwritten public offering
of securities by the Company, the Holder hereof shall have the right to convert
this Warrant or any portion hereof into Warrant Stock by executing and
delivering to the Company at its principal office the written Notice of
Conversion and Investment Representation Statement in the forms attached hereto
as ATTACHMENTS 2 AND 3, specifying the portion of the Warrant to be converted,
and accompanied by this Warrant. The number of shares of Warrant Stock to be
issued to Holder upon such conversion shall be computed using the following
formula:

                                 X=(P)(Y)(A-B)/A

         where X =         the number of shares of Warrant Stock to be issued to
                           the Holder for the portion of the Warrant being
                           converted.

                           P =      the portion of the Warrant being converted
                                    expressed as a decimal fraction.

                           Y =      the total number of shares of Warrant Stock
                                    issuable upon exercise of the Warrant in
                                    full.

                           A =      the fair market value of one share of
                                    Warrant Stock which means (i) the fair
                                    market value of the Warrant Stock as of the
                                    last Business Day immediately prior to the
                                    date the notice of conversion is received by
                                    the Company, as reported in the principal
                                    market for such securities or, if no such
                                    market exists, as determined in good faith
                                    by the Company's Board of Directors, or (ii)
                                    if this Warrant is being converted in
                                    conjunction with a public offering of stock
                                    the price to the public per share pursuant
                                    to the offering.

                           B =      the Warrant Price on the date of conversion.

Any portion of this Warrant that is converted shall be immediately canceled.
This Warrant or any portion hereof shall be deemed to have been converted
immediately prior to the close of business on the date of its surrender for
conversion as provided above, and the person entitled to receive the shares of
Warrant Stock issuable upon such conversion shall be treated for all purposes as
the holder of such shares of record as of the close of business on such date. As
promptly as practicable after such date, the Company shall issue and deliver to
the person or persons entitled to receive the same a certificate or certificates
for the number of full shares of Warrant Stock issuable upon such conversion. If
the Warrant shall be converted for less than the

                                      -7-
<PAGE>

total number of shares of Warrant Stock then issuable upon conversion, promptly
after surrender of the Warrant upon such conversion, the Company will execute
and deliver a new warrant, dated the date hereof, evidencing the right of the
Holder to the balance of the Warrant Stock purchasable hereunder upon the same
terms and conditions set forth herein. If this Warrant is converted, as a whole
or in part, after the occurrence of a Change-In-Control Event as to which
Section 3(c) is applicable, the Holder shall receive the consideration
contemplated by Section 3(c) in lieu of Warrants Stock of the Company.

         8. TRANSFER OF WARRANT. This Warrant may be transferred or assigned by
the Holder hereof as a whole or in part, provided that the transferor provides,
at the Company's request, an opinion of counsel satisfactory to the Company that
such transfer does not require registration under the Securities Act and the
securities law applicable with respect to any other applicable jurisdiction.

         9. TERMINATION. This Warrant shall terminate on 5:00 p.m. New York time
on the Termination Date.

         10. MISCELLANEOUS. This Warrant shall be governed by the laws of the
Commonwealth of Massachusetts, as such laws are applied to contracts to be
entered into and performed entirely in Massachusetts by Massachusetts residents.
In the event of any dispute among the Holder and the Company arising out of the
terms of this Warrant, the parties hereby consent to the exclusive jurisdiction
of the federal and state courts located in the Commonwealth of Massachusetts for
resolution of such dispute, and agree not to contest such exclusive jurisdiction
or seek to transfer any action relating to such dispute to any other
jurisdiction. The headings in this Warrant are for purposes of convenience and
reference only, and shall not be deemed to constitute a part hereof. Neither
this Warrant nor any term hereof may be changed or waived orally, but only by an
instrument in writing signed by the Company and the Holder of this Warrant. All
notices and other communications from the Company to the Holder of this Warrant
shall be delivered personally or by facsimile transmission or mailed by first
class mail, postage prepaid, to the address or facsimile number furnished to the
Company in writing by the last Holder of this Warrant who shall have furnished
an address or facsimile number to the Company in writing, and if mailed shall be
deemed given three days after deposit in the United States mail.

                                      -8-
<PAGE>

         ISSUED:  April 21, 2000

                  BEACON POWER CORPORATION

                  By:__________________________________

                  Name:    William E. Stanton

                  Title:   President

                                      -9-
<PAGE>

                                  Attachment 1

NOTICE OF EXERCISE

TO:      BEACON POWER CORPORATION

1.   The undersigned hereby elects to purchase _______________ shares of the
     Warrant Stock of Beacon Power Corporation pursuant to the terms of the
     attached Warrant, and tenders herewith payment of the purchase price in
     full, together with all applicable transfer taxes, if any.

2.   Please issue a certificate or certificates representing said shares of
     Warrant Stock in the name of the undersigned or in such other name as is
     specified below:

                         ------------------------------
                                     (Name)

                         -------------------------------
                                    (Address)

---------------------------------------     -----------------------------------
(Date)   (Name of Warrant Holder)

   By:_________________________________

   Title:______________________________

<PAGE>

                                  Attachment 2

                       INVESTMENT REPRESENTATION STATEMENT

                      Shares of the Class F Preferred Stock
                     (as defined in the attached Warrant) of
                            BEACON POWER CORPORATION

         In connection with the purchase of the above-listed securities, the
undersigned hereby represents to Beacon Power Corporation (the "Company") as
follows:

(a) The securities to be received upon the exercise of the Warrant (the
"Securities") will be acquired for investment for its own account, not as a
nominee or agent, and not with a view to the sale or distribution of any part
thereof, and the undersigned has no present intention of selling, granting
participation in or otherwise distributing the same, but subject, nevertheless,
to any requirement of law that the disposition of its property shall at all
times be within its control. By executing this statement, the undersigned
further represents that it does not have any contract, undertaking, agreement or
arrangement with any person to sell, transfer, or grant participations to such
person or to any third person, with respect to any Securities issuable upon
exercise of the Warrant.

(b) The undersigned understands that the Securities issuable upon exercise of
the Warrant at the time of issuance may not be registered under the Securities
Act of 1933, as amended (the "Securities Act"), and applicable state securities
laws, on the ground that the issuance of such securities is exempt pursuant to
Section 4(2) of the Securities Act and state law exemptions relating to offers
and sales not by means of a public offering, and that the Company's reliance on
such exemptions is predicated on the undersigned's representations set forth
herein.

(c) The undersigned agrees that in no event will it make a disposition of any
Securities acquired upon the exercise of the Warrant unless and until (i) it
shall have notified the Company of the proposed disposition and shall have
furnished the Company with a statement of the circumstances surrounding the
proposed disposition, and (ii) it shall have furnished the Company with an
opinion of counsel satisfactory to the Company and Company's counsel to the
effect that (A) appropriate action necessary for compliance with the Securities
Act and any applicable state securities laws has been taken or an exemption from
the registration requirements of the Securities Act and such laws is available,
and (B) the proposed transfer will not violate any of said laws.

(d) The undersigned acknowledges that an investment in the Company is highly
speculative and represents that it is able to fend for itself in the
transactions contemplated by this statement, has such knowledge and experience
in financial and business matters as to be capable of evaluating the merits and
risks of its investments, and has the ability to bear the economic risks
(including the risk of a total loss) of its investment. The undersigned
represents that it has had the opportunity to ask questions of the Company
concerning the Company's business and assets and to obtain any additional
information which it considered necessary to verify the accuracy of or to

<PAGE>

amplify the Company's disclosures, and has had all questions which have been
asked by it satisfactorily answered by the Company

(e) The undersigned acknowledges that the Securities issuable upon exercise or
conversion of the Warrant must be held indefinitely unless subsequently
registered under the Securities Act or an exemption from such registration is
available. The undersigned is aware of the provisions of Rule 144 promulgated
under the Securities Act which permit limited resale of shares purchased in a
private placement subject to the satisfaction of certain conditions, including,
among other things, the existence of a public market for the shares, the
availability of certain current public information about the Company, the resale
occurring not less than one year after a party has purchased and paid for the
security to be sold from the Company or any affiliate of the Company, the sale
being through a "broker's transaction" or in transactions directly with a
"market maker" (as provided by Rule 144(f)) and the number of shares being sold
during any three month period not exceeding specified limitations.

         Dated:________________________

         _______________________________________
         (Typed or Printed Name)

         By:____________________________________
              (Signature)

         _______________________________________
         (Title)

<PAGE>

                                  Attachment 3

NOTICE OF CONVERSION

TO:      BEACON POWER CORPORATION

1. The undersigned hereby elects to acquire _______________ shares of the
Warrant Stock of Beacon Power Corporation pursuant to the terms of the attached
Warrant, by conversion of _________ percent (_____%) of the Warrant.

2. Please issue a certificate or certificates representing said shares of
Warrant Stock in the name of the undersigned or in such other name as is
specified below:

                         ------------------------------
                                     (Name)

                         -------------------------------
                                    (Address)

---------------------------------------     -----------------------------------
(Date)   (Name of Warrant Holder)

     By:________________________________

     Title:_______________________________
        (Title and signature of authorized person)

<PAGE>

                      WARRANTS OF BEACON POWER CORPORATION

                   ISSUED PURSUANT TO CLASS F BRIDGE FINANCING

<TABLE>
<CAPTION>
----------------------------------------------------- ---------------------------------------------------------
                      Name of Holder                    Number of shares of common stock underlying warrant
----------------------------------------------------- ---------------------------------------------------------
<S>                                                   <C>
Perseus Capital, L.L.C.                                                        12,000
----------------------------------------------------- ---------------------------------------------------------
Micro-Generation Technology Fund, L.L.C.                                       4,000
----------------------------------------------------- ---------------------------------------------------------
Mechanical Technology, Inc.                                                    12,000
----------------------------------------------------- ---------------------------------------------------------
The Beacon Group Energy Investment II, L.P.                                    9,000
----------------------------------------------------- ---------------------------------------------------------
Penske Corporation                                                             4,000
----------------------------------------------------- ---------------------------------------------------------
</TABLE>

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