381/391 (SR1120) Watch Batteries
These button cells are 1.55V batteries, used chiefly in low-drain applications like simple wrist watches. They feature a large case, with a medium-high capacity. 381/391 batteries will replace cells with these numbers: 381, SR1120SW, SR55, RW30, D381, V381(533), 28027, SB-AS, 391, SR1120W, SR55W, RW40, D391, V391(553), 28030, SB-BS.
Silver oxide chemistry gives these batteries a typical capacity in the 50mAh range. The case measures 11.6mm x 2.05mm.