Abstract: Described herein is a flexible battery pack for powering downhole electronic equipment. The pack includes a plurality of electrochemical cells connected and tied together in a stacked working relationship by a pair of semi cylindraceous encapsulating shells which form a primary containment for the electrochemical cells. The shells are secured at each end to a cylindrical insulating plug which secures the shells together. The shells preferably comprise a glass fiber reinforced plastic material. The primary containment is then sealed in a stainless steel tube which is provided to hold the interior components in place during operation. The encapsulating members are provided with an internal grooved recess which receives and holds any electrical conductors which may be required for operation of the battery pack.