Exhibit 5

                                 August 17, 2001

Ultralife Batteries, Inc.
2000 Technology Parkway
Newark, New York 14513

      Re:   Ultralife Batteries, Inc.
            Registration Statement on Form S-3

Ladies and Gentlemen:

      You have requested our opinion in connection with your Registration
Statement on Form S-3, filed under the Securities Act of 1933, as amended, with
the Securities and Exchange Commission (the "Registration Statement"), in
respect of a resale offering of an aggregate of 1,090,000 authorized and issued
shares of the Common Stock, par value $.10 per share (the "Common Stock"), of
Ultralife Batteries, Inc. (the "Corporation"), which may be sold by certain
stockholders of the Corporation and 109,000 shares of Common Stock to be issued
upon the exercise of certain warrants to purchase the Corporation's Common
Stock.

      We have examined the following corporate records and proceedings of the
Corporation in connection with the preparation of this opinion: its Certificate
of Incorporation; its By-laws as currently in force and effect; its Minute
Books, containing minutes and records of other proceedings of its stockholders
and its Board of Directors, from the date of incorporation to the date hereof;
the Registration Statement; applicable provisions of the laws of the State of
Delaware; and such other documents and matters as we have deemed necessary.

      In rendering this opinion, we have made such examination of laws as we
have deemed relevant for the purposes hereof. As to various questions of fact
material to this opinion, we have relied upon representations and/or
certificates of officers of the Corporation, certificates and documents issued
by public officials and authorities, and information received from searchers of
public records.

      Based upon and in reliance on the foregoing, we are of the opinion that:

            1. The Corporation has been duly incorporated and is validly
      existing under the laws of the State of Delaware.

            2. The Corporation had the authority to issue an aggregate of
      1,090,000 shares of Common Stock and to authorize the issuance of an
      aggregate 109,000 shares of Common Stock upon exercise of the warrants.

            3. The 1,090,000 shares of Common Stock issued by the Corporation
      and registered pursuant to the Registration Statement were legally and
      validly issued, and are fully paid and non-assessable, and the warrants
      have been legally and validly issued, and upon issuance in accordance with
      the terms and provisions of the warrants, the shares of Common Stock
      issued upon exercise of the warrants will be legally and validly issued,
      and will be fully paid and non-assessable.

      We hereby consent to be named in the Registration Statement as attorneys
passing upon legal matters in connection with the registration of the 1,199,000
shares of Common Stock covered thereby, and we hereby consent to the filing of
this opinion as Exhibit 5 to the Registration Statement.

                                          Very truly yours,

                                          /s/ HARTER, SECREST & EMERY LLP