Document:

<PAGE>

                                                                 Exhibit 10.1.10

         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 OR OFFERED FOR SALE OR OTHERWISE
DISTRIBUTED UNLESS THERE IS AN EFFECTIVE REGISTRATION STATEMENT UNDER THE
SECURITIES ACT COVERING SUCH SECURITIES, THE SALE IS MADE IN COMPLIANCE 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 OR ASSIGNMENT IS EXEMPT FROM THE REGISTRATION AND
PROSPECTUS DELIVERY REQUIREMENTS OF THE SECURITIES 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 INVESTORS RIGHTS AGREEMENT BY AND AMONG THE COMPANY AND CERTAIN
STOCKHOLDERS 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 May 23, 2005)

         1. ISSUANCE OF WARRANT. FOR VALUE RECEIVED, from and after the
Commencement Time, 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
City time on May 23, 2005 (the "Termination Date"), the Warrant Stock (as
defined below) at a price per share equal to the Warrant Price (as defined
below) upon exercise of 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) "Business Day" means any day other than a Saturday, Sunday or other
day on which the national or state banks located in the Commonwealth of
Massachusetts, the State of New York or the District of Columbia are authorized
to be closed.

         (b) "Commencement Time" means immediately prior to the consummation of
a Liquidity Event.

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

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

<PAGE>

         (e) "Liquidity Event" means (i) the consummation of the sale or other
disposition of all or substantially all of the assets of the Company to another
Person or the acquisition of at least a majority of the outstanding voting stock
of the Company by another Person by means of a merger, consolidation or
otherwise, in either case on financial terms that reflect a total equity value
of at least $200 million for the Company immediately prior to the consummation
of such transaction (a "Sale Transaction") or (ii) the consummation of an
underwritten public offering of Common Stock pursuant to an effective
registration statement under the Securities Act of 1933, as amended, that (a)
results in the Company receiving at least $30 million in gross proceeds and (b)
is made at an initial offering price per share (the "Initial Price") that
reflects a market capitalization value of at least $200 million for the Company
(a "Qualified Public Offering").

         (f) "Person" means any individual, corporation, partnership, limited
liability company, or other entity.

         (g) "Securities Purchase Agreement" means the Securities Purchase
Agreement dated as of May 23, 2000 by and among the Company, Perseus Capital,
L.L.C., DQE Enterprises, Inc., Micro Generation Technology Fund, L.L.C., GE
Capital Equity Investments, Inc., Mechanical Technologies Incorporated, Penske
Corporation, and The Beacon Group, LLC (collectively, the "Purchasers").

         (h) "Warrant Price" means 75% of the lower of (i) the effective price
per share of Common Stock paid by the acquirer in a Sale Transaction as
determined by a nationally recognized investment banking firm chosen by the
Company and approved by Purchasers that hold a majority of the aggregate
Preferred Shares and Conversion Shares (as such terms are defined in the
Securities Purchase Agreement) as of the date of consummation of such Sale
Transaction and (ii) the Initial Price in first Qualified Offering, in each case
subject to adjustment under Section 3.

         (i) "Warrant Stock" means a number of shares of Common Stock equal to
the quotient obtained by dividing (i) 50% of the aggregate stated value of the
Preferred Shares acquired by the initial Holder of this Warrant pursuant to the
Securities Purchase Agreement by (ii) the Warrant Price, subject to adjustment
under Section 3.

         (j) "Warrant Stock Class" means the class of capital stock or other
securities that includes the Warrant Stock.

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

         (a) SUBDIVISION, STOCK DIVIDENDS OR COMBINATIONS. In case the Company
shall at any time subdivide the outstanding shares of the Warrant Stock Class or
shall issue a stock dividend with respect to the Warrant Stock Class, 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 Class, 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 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 the Warrant Stock Class, 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.

                                      -2-
<PAGE>

         (c) REORGANIZATION, MERGER ETC. In case of any (i) merger or
consolidation of the Company into or with another corporation where the Company
is not the surviving corporation, (ii) sale, transfer or lease (but not
including a transfer or lease by pledge or mortgage to a bona fide lender) of
all or substantially all of the assets of the Company or (iii) sale by the
Company's shareholders of 50% or more of the Company's outstanding securities in
one or more related transactions, 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
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 transactions of the
type described in this subparagraph (c).

         (d) 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.

         (e) 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 Warrant Stock Class other than as
described above that adversely affects the Holder's rights under this Warrant,
the Warrant Price shall be adjusted downward.

         (f) 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. 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 from and after the Commencement Time and 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

                                      -3-
<PAGE>

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 the 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 from and after the Commencement Time and prior to the
termination of this Warrant, 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 the
                                    Warrant Stock Class which means (i) the fair
                                    market value of one share of the Warrant
                                    Stock Class 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
                                    Liquidity Event, 133.33% of the Warrant
                                    Price then in effect.

                           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 converted, as a
whole or in part, after the occurrence of a transaction as to which Section 3(c)
is applicable, the Holder shall receive the consideration contemplated by
Section 3(c) in lieu of Warrant Stock of the Company.

         8. NOTICE OF LIQUIDITY EVENT.The Company shall provide the Holder with
at least 10 Business Days advance written notice prior to the consummation of
any Liquidity Event describing in reasonable detail the terms and conditions of
such Liquidity Event and an estimate of the Warrant Price derivable from such
Liquidity Event.

                                      -4-
<PAGE>

         9. 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.

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

         11. MISCELLANEOUS. This Warrant shall be governed by the laws of the
State of Delaware, as such laws are applied to contracts to be entered into and
performed entirely in Delaware by Delaware residents. 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.

                                      -5-
<PAGE>

ISSUED:  May 23, 2000

         BEACON POWER CORPORATION

         By:__________________________________

         Name:    William E. Stanton

         Title:   President

                                      -6-
<PAGE>

                                  Attachment 1

NOTICE OF EXERCISE

TO:      BEACON POWER CORPORATION

1.       The undersigned hereby elects to purchase _______________ shares of
         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

         In connection with the purchase of the shares of Warrant Stock upon
exercise of the enclosed Warrant, 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
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)

<PAGE>

By:___________________________
          (Signature)

______________________________
(Name)

______________________________
(Title)

                                  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 FINANCING

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

------------------------------------------------------- ---------------------------------------------------------
<S>                                                     <C>
Perseus Capital, L.L.C.

------------------------------------------------------- ---------------------------------------------------------
DQE Enterprises, Inc.

------------------------------------------------------- ---------------------------------------------------------
Micro-Generation Technology Fund, L.L.C.

------------------------------------------------------- ---------------------------------------------------------
Mechnical Technology, Inc.

------------------------------------------------------- ---------------------------------------------------------
GE Capital Equity Investments, Inc.

------------------------------------------------------- ---------------------------------------------------------
The Beacon Group Energy Investment Fund II,. L.P

------------------------------------------------------- ---------------------------------------------------------
Peske Corporation

------------------------------------------------------- ---------------------------------------------------------
</TABLE><PAGE>

                                                                 Exhibit 10.1.11

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 OR OFFERED FOR SALE OR OTHERWISE DISTRIBUTED
UNLESS THERE IS AN EFFECTIVE REGISTRATION STATEMENT UNDER THE SECURITIES ACT
COVERING SUCH SECURITIES, THE SALE IS MADE IN COMPLIANCE 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 OR ASSIGNMENT IS EXEMPT FROM THE REGISTRATION AND PROSPECTUS DELIVERY
REQUIREMENTS OF THE SECURITIES 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 INVESTORS RIGHTS AGREEMENT BY AND AMONG THE COMPANY AND CERTAIN
STOCKHOLDERS OF THE COMPANY. A COPY OF SUCH AGREEMENT IS ON FILE AT THE
PRINCIPAL OFFICE OF THE COMPANY.

No.: CC-1

                                     WARRANT
                            TO PURCHASE COMMON STOCK
                                       OF
                            BEACON POWER CORPORATION

                          (void after February 2, 2001)

         1. ISSUANCE OF WARRANT. FOR VALUE RECEIVED, at the Commencement
Time, 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 the Commencement Time and before
5:00 p.m. New York City time on February 2, 2001 (the "Termination Date"),
50,000 shares of the Warrant Stock (as defined below) at a price per share
equal to the Warrant Price (as defined below) upon exercise of this Warrant
pursuant to Section 6 hereof.

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

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

                  (b) "Commencement Time" means immediately prior to the
consummation of

<PAGE>

a Liquidity Event.

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

                  (d) "Holder" means Cox Communications, Inc., or its assigns.

                  (e) "Liquidity Event" means the consummation of an
underwritten public offering of Common Stock pursuant to an effective
registration statement under the Securities Act of 1933, as amended (a "Public
Offering").

                  (f) "Person" means any individual, corporation, partnership,
limited liability company, or other entity.

                  (g) "Warrant Price" means the initial offering price per share
of the Common Stock in the first Public Offering, in each case subject to
adjustment under Section 3.

                  (h) "Warrant Stock" means the Common Stock.

                  (i) "Warrant Stock Class" means the class of capital stock or
other securities that includes the Warrant Stock.

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

                  (a) SUBDIVISION, STOCK DIVIDENDS OR COMBINATIONS. In case the
Company shall at any time subdivide the outstanding shares of the Warrant Stock
Class or shall issue a stock dividend with respect to the Warrant Stock Class,
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
Class, 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 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 the Warrant Stock Class, 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

                                      -2-
<PAGE>

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 (i) merger or
consolidation of the Company into or with another corporation where the Company
is not the surviving corporation, (ii) sale, transfer or lease (but not
including a transfer or lease by pledge or mortgage to a bona fide lender) of
all or substantially all of the assets of the Company or (iii) sale by the
Company's shareholders of 50% or more of the Company's outstanding securities in
one or more related transactions, 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
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 transactions of the
type described in this subparagraph (c).

                  (d) 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.

                  (e) 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 Warrant Stock Class other than as
described above that adversely affects the Holder's rights under this Warrant,
the Warrant Price shall be adjusted downward.

                  (f) FRACTIONAL SHARES. No fractional shares shall be issuable
upon exercise or

                                      -3-
<PAGE>

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. 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 the Commencement Time and 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 the Warrant Stock purchasable hereunder upon the
same terms and conditions set forth herein.

         7. NOTICE OF LIQUIDITY EVENT.The Company shall provide the Holder with
at least 10 Business Days advance written notice prior to the consummation of
any Liquidity Event describing in reasonable detail the terms and conditions of
such Liquidity Event and an estimate of the Warrant Price derivable from such
Liquidity Event.

         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.

                                      -4-
<PAGE>

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

         10. LOCK-UP. The Holder will not, without the prior written consent of
Salomon Smith Barney Inc., offer, sell, contract to sell, pledge or otherwise
dispose of (or enter into any transaction which is designed to, or might
reasonably be expected to, result in the disposition (whether by actual
disposition or effective economic disposition due to cash settlement or
otherwise) by the undersigned or any affiliate of the Holder or any person in
privity with the Holder or any affiliate of the Holder), directly or indirectly,
including the filing of a registration statement with the Securities and
Exchange Commission in respect of, or establish or increase a put equivalent
position or liquidate or decrease a call equivalent position within the meaning
of Section 16 of the Securities Exchange Act of 1934, as amended, and the rules
and regulations of the Securities and Exchange Commission promulgated hereunder
with respect to, any shares of capital stock of the Company or any securities
convertible into, or exercisable or exchangeable for such capital stock, or
publicly announce an intention to effect any such transaction, for a period of
180 days after the date of the proposed Underwriting Agreement (the
"Underwriting Agreement"), between the Company, and each of the Underwriters
named therein, other than shares of Common Stock disposed of as bona fide gifts
approved by Salomon Smith Barney Inc. If for any reason the Underwriting
Agreement shall be terminated prior to the Closing Date (as defined in the
Underwriting Agreement), this provision shall be of no further effect.

         11. MISCELLANEOUS. This Warrant shall be governed by the laws of the
State of Delaware, as such laws are applied to contracts to be entered into and
performed entirely in Delaware by Delaware residents. 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.

                                      -5-
<PAGE>

         ISSUED:  AUGUST 2, 2000

                  BEACON POWER CORPORATION

                  By:      /s/ William E. Stanton
                           ------------------------

                  Name:    William E. Stanton

                  Title:   President

                                      -6-
<PAGE>

                                  Attachment 1

NOTICE OF EXERCISE

TO:      BEACON POWER CORPORATION

1.   The undersigned hereby elects to purchase _______________ shares of 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

         In connection with the purchase of the shares of Warrant Stock upon
exercise of the enclosed Warrant, 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
amplify the Company's disclosures, and has had all questions which have been
asked by it satisfactorily answered by the Company

<PAGE>

(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)

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

         ---------------------------------------
         (Title)

                                      -2-

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