<PAGE>

                                                                     Exh 10.1.12

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.

No.:  KP-1


                                     WARRANT
                            TO PURCHASE COMMON STOCK
                                       OF
                            BEACON POWER CORPORATION

                           (void after August 2, 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 August 2, 2005 (the "Termination Date"), at a price per
share equal to (the Warrant Price) (as defined below and subject to adjustment
as described below), 20,000 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)   "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 a Liquidity Event.

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

            (d)   "Holder" means Kaufman-Peters Company, 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.
<PAGE>

            (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)   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 (a) shall similarly apply to successive transactions of the
type described in this subparagraph (a).

            (b)   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.

            (c)   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.

            (d)   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.


                                      -2-
<PAGE>

      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.

      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 Holder or any affiliate of the Holder or any person in privity
with the Holder or any affiliate of the Holder), directly or indirectly, in 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, in connection
with the Company's pending initial public offering, 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


                                      -3-
<PAGE>

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.

                                      ISSUED:  August 2, 2000



                                               BEACON POWER CORPORATION

                                               By:      /s/ William E. Stanton

                                               Name:    William E. Stanton

                                               Title:   President



                                      -4-
<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:________________________
<PAGE>

         ---------------------------------------
         (Typed or Printed Name)

         By:____________________________________
              (Signature)

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



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