Here you can found some information's about the Praktica batteries.

type	picture	properties / availability
V 625 PX		1.35 V mercury oxide-battery production stopped replacement:  Z625PX (1.4V, zinx-air battery) V 625 U (1.5 V, alkaline battery) both works without any alteration of the measurement results of the light meter
V 625 PC adapter
V PX 21		4.5 V mercury oxide battery production stopped   replacement:  use standard battery CR 123 A 3,0 V with a special adapter which you can get through PRAKTICA (www.praktica.de, Pentacon GmbH, Praktica-Service, Foto- und Feinwerktechnik, Enderstr. 94, 01277 Dresden, Tel.: 0351/2589230) or www.radioshack.com product number 960-0357 4.5V (Alkaline) Photo Battery ($6.99) or replace the PX21 by 3xLR50-battery wrapping with shrinkdown plastic tubing
V 28 PX (4SR44)		6.2 V silver battery production stopped replacement:  4LR44 Alkaline (mangan) battery or www.radioshack.com product number 960-1190 6V (Silver Oxide) Photo  Battery ($11.99)