Document:

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                                                                     Exhibit 4.1

                           METRETEK TECHNOLOGIES, INC.
                            1675 BROADWAY, SUITE 2150
                             DENVER, COLORADO 80202
                                 (303) 592-5555

             NOTICE OF REDEMPTION OF COMMON STOCK PURCHASE WARRANTS

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                        REDEMPTION DATE: AUGUST 14, 2000

            EXERCISE RIGHT EXPIRES: 5:00 P.M., DENVER, COLORADO TIME

                                 AUGUST 14, 2000
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TO THE HOLDERS OF
COMMON STOCK PURCHASE WARRANTS OF
METRETEK TECHNOLOGIES, INC.:

         NOTICE IS HEREBY GIVEN that, pursuant to the provisions of the Warrant
Agency Agreement, dated as of September 10, 1998 (the "Warrant Agreement"),
between Metretek Technologies, Inc. (formerly known as Marcum Natural Gas
Services, Inc.) ("Metretek") and Computershare Trust Company, Inc., (formerly
known as American Securities Transfer & Trust, Inc.) (the "Warrant Agent"),
Metretek hereby exercises its right to redeem all Common Stock Purchase Warrants
issued under the Warrant Agreement (the "Warrants") that remain outstanding and
unexercised at 5:00 p.m., Denver, Colorado time, on August 14, 2000 (the
"Redemption Date"), the date fixed for redemption, at a redemption price of $.01
per Warrant (the "Redemption Price"). All conditions to and requirements for
Metretek's redemption of the Warrants have been met.

         Each Warrant entitles the holder thereof to purchase one share of
Common Stock, par value $.01 per share ("Common Stock"), of Metretek at an
exercise price of $4.00 per share, subject to adjustment in certain events, at
any time until 5:00 p.m., Denver, Colorado time, on the Redemption Date, and the
Warrants will remain exercisable pursuant to the terms of the Warrant Agreement
until such date and time. The exercise of the Warrants is covered by Metretek's
Registration Statement on Form S-3, Registration No. 333-60925 as amended (the
"Registration Statement"). For further information regarding the Warrants,
including the method of exercise thereof, you are advised to refer to Metretek's
Prospectus dated July 14, 2000.

         The Warrants are traded on the Nasdaq SmallCap Market under the trading
symbol "MTEKW". The Warrants will cease trading after the Redemption Date. The
Common Stock is traded on the Nasdaq National Market under the trading symbol
"MTEK". On July 11, 2000, the last sale price of the Common Stock as reported on
the Nasdaq National Market was $6.06 per share and the last sale price of the
Warrants as reported on the Nasdaq SmallCap Market was $2.63 per Warrant.

         This Notice is accompanied by the following: (i) Metretek's Annual
Report on Form 10-KSB for the year ended December 31, 1999; (ii) Metretek's Form
10-QSB for the fiscal quarter ended March 31, 2000; and (iii) the Prospectus,
dated July 14, 2000, covering the exercise of the warrants. Additional copies of
this Notice, the Prospectus or the other documents included with this Notice may
be obtained, without charge, by written or oral request to Metretek at the
address and telephone number set forth above.

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                  ALTERNATIVES AVAILABLE TO HOLDERS OF WARRANTS

         As a result of Metretek's election to redeem the Warrants, Warrant
holders have the following three alternatives with respect to their warrants:

-    Holders may exercise their Warrants. Until 5:00 p.m., Denver, Colorado
     time, on August 14, 2000, when the exercise right expires, Warrant holders
     may exercise their Warrants by purchasing shares of Common Stock at the
     exercise price of $4.00 per share.

-    Holders may sell their Warrants in the open market. Until 5:00 p.m.,
     Denver, Colorado time, on the Redemption Date, holders may sell their
     Warrants in the open market through brokers or otherwise. Until the
     Redemption Date, the Warrants will continue to trade on the Nasdaq SmallCap
     Market under the trading symbol "MTEKW". The Warrants will cease trading
     after the Redemption Date.

-    Holders may deliver their Warrants to be redeemed for cash. After 5:00
     p.m., Denver, Colorado time, on the Redemption Date, any Warrants that
     holders continue to hold will be redeemed by Metretek at a Redemption Price
     of $.01 per Warrant. All Warrants outstanding on or after the Redemption
     Date will be deemed to be redeemed by Metretek, whether or not they have
     been surrendered for redemption. However, Warrant holders must surrender
     their Warrants to the Warrant Agent, as discussed below, to collect the
     Redemption Price.

         Holders of Warrants are urged to consult with their own tax, business
and other advisors concerning the tax, business and other consequences of the
exercise, sale or redemption of their Warrants.

                         MANNER OF EXERCISE OF WARRANTS

         Warrant holders may exercise the Warrants by properly completing and
signing the subscription form on the Warrants including, if required, a
signature guarantee from an eligible institution, and mailing or delivering the
Warrants to the Warrant Agent, together with a payment of the aggregate exercise
price of the Warrants in full (in U.S. dollars) by such holder, to:

                        Computershare Trust Company, Inc.
                      12039 West Alameda Parkway, Suite Z-2
                            Lakewood, Colorado 80228
                            Telephone: (303) 986-5400
                            Facsimile: (303) 986-2444

                                     or to:

                        Computershare Trust Company, Inc.
                                  P.O. Box 1596
                              Denver, CO 80201-1596

A holder may exercise Warrants in whole or in part, but no Warrants may be
exercised for fractional shares of Common Stock.

         The exercise price will be considered to have been paid only upon
clearance of the wire transfer, certified or official bank check, bank draft or
money order tendered therefor. All funds received by the Warrant Agent from the
exercise of the Warrants will be deposited upon receipt. Pending issuance of
certificates representing shares of Common Stock, funds received for the
exercise of Warrants will be held in a segregated escrow account.

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         ONCE A HOLDER HAS EXERCISED A WARRANT, THE EXERCISE MAY NOT BE REVOKED.
To be accepted, the properly completed Warrants and payment with respect to the
exercise price of the Warrants must be received by the Warrant Agent before 5:00
p.m., Denver, Colorado time on August 14, 2000. The instruction accompanying the
Warrants should be read carefully and followed in detail. WARRANTS SHOULD BE
SENT WITH PAYMENT TO THE WARRANT AGENT. DO NOT SEND WARRANTS TO METRETEK.

         CERTIFICATES REPRESENTING THE SHARES OF COMMON STOCK SUBSCRIBED FOR
WILL BE ISSUED AND DELIVERED AS SOON AS PRACTICABLE AFTER PAYMENT OF THE
EXERCISE PRICE OF THE WARRANTS. HOLDERS OF WARRANTS, AS SUCH, WILL NOT HAVE ANY
RIGHTS AS STOCKHOLDERS OF THE COMPANY UNTIL STOCK CERTIFICATES REPRESENTING THE
SHARES OF COMMON STOCK SUBSCRIBED FOR ARE ISSUED TO THEM.

         The risk of method of delivery of all documents and payment is on the
holders of the Warrants, not Metretek or the Warrant Agent. If the mail is used,
it is recommended that payments be made by registered mail, properly insured,
return receipt requested, and that a sufficient number of days be allowed to
ensure delivery to the Warrant Agent before the expiration of the Warrants.

         Stifel, Nicolaus & Company, Inc. (the "Dealer Manager") will serve as
the dealer manager and will contact warrant holders, explain the terms of the
proposed redemption to Warrant holders, and solicit holders to exercise their
Warrants. The Dealer Manager's address is:

                        Stifel, Nicolaus & Company, Inc.
                          1125 17th Street, Suite 1500
                             Denver, Colorado 80202
                            Telephone: (303) 296-2300

         Questions relating to the method of exercise should be directed to the
Warrant Agent or the Dealer Manager at the addresses set forth above.

         The right of holders to exercise the Warrants will expire at 5:00 p.m.,
Denver, Colorado time, on the Redemption Date. All Warrants not properly
exercised on or before such date and time will be redeemed by Metretek at the
Redemption Price. Prior to the Redemption Date, Metretek will deposit with the
Warrant Agent an amount sufficient to pay the Redemption Price for all Warrants
called for redemption. After the Redemption Date, all Warrant Certificates
evidencing the Warrants must be delivered to the Warrant Agent at the address
set forth above for receipt of the Redemption Price.

         The Warrants were issued pursuant to, and the method of exercise and
redemption and the rights of the holders Warrants are governed by and subject
to, the terms and conditions of the Warrant Agreement. This Notice of Redemption
is being given, and the manner of redemption will be conducted, in compliance
with the terms and conditions of the Warrant Agreement. A copy of the Warrant
Agreement is available for inspection, and will be furnished to holders of
Warrants, without charge, upon written or oral request to the Warrant Agent at
the address set forth above.

                                         By Order of the Board of Directors

                                         W. Phillip Marcum, President

Denver, Colorado
July 14, 2000<PAGE>   1
                                                               Exhibit 10.1.13.a

June 15, 2000

Mr. David H. Biggs
896 Bollen Circle
Gardnerville, Nevada 89410

Dear David:

I am pleased to offer you some changes in the status in your exempt position of
Vice-President, Chief Technical Officer for Telxon Corp. in The Woodlands, Texas
office. Effective 15 June 2000, the terms of the agreement between you and
Telxon are:

1.   Starting on 7 August 2000, your bi-weekly salary will be $9,615.38, which
     equates to $250,000.00 annualized.

2.   You will continue to report to Ken Cassady, President & COO.

3.   Telxon Corporation is in the process of revising its corporate incentive
     compensation program based on overall company profitability and increased
     revenue. As Vice-President, Chief Technical Officer, you would be eligible
     under such a plan, after final approval, for an annual incentive
     compensation opportunity of 35%.

4.   You are eligible to receive a grant of 50,000 options under the Telxon
     Corporate Stock Option Plan, which options shall vest in equal amounts
     over a three year period from the initial grant date. The options are
     subject to the approval of the Chairman of the Board and the Compensation
     Committee of the Board of Directors.

5.   You are eligible to participate in Telxon's insurance plans, including
     medical, dental, accident and life, upon hire. You are also eligible to
     participate in Telxon's profit sharing 401(k) plan during the next open
     enrollment period.

6.   You are eligible for four weeks of vacation, annually. Your vacation
     allocation for calendar year 2000 will be pro-rated accordingly.

7.   Your living expenses will continue to be covered in accordance with your
     original employment agreement, dated June 7, 1999.

8.   You will receive a one-year severance ($250,000.00) in the event of a
     "Change-in Control" as defined in section 4.c.ii. of your original
     employment agreement, dated June 7, 1999.

9.   You will receive a six-month severance ($125,000.000) if you should leave
     Telxon after 7 August 2001. The six-month severance will be paid only if
     you assist Telxon in finding and training a qualified replacement for Vice
     President, Chief Technical Officer.

10.  You have discussed this position with Ken Cassady and understand the duties
     and responsibilities associated with it. It is Telxon's intention and
     expectation that you will fulfill those duties and responsibilities without
     violating any legal obligations you may have to your former employers.

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We look forward to the prospect of your continued relationship with Telxon
Corporation, David. Should you have any questions or need additional
information, please contact me at (800) 800-8013, Extension 5815.

Sincerely,

/s/ Ken Cassady
Ken Cassady
President & COO

Enclosure

cc:    John Paxton
       Cecile Hickman
       Mitch Herrod

I accept the terms of this agreement.

Signature /s/ David H. Biggs.
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