CX521S, V379, SR63, LR521, SR521, Silver Oxide Button Cell  1.55V High Capacity.

Typically for watches & calculators and miniature equipment 5.8 X 2.1mm. Equivalent to V379, SR63, LR521, SR521, GP379, 618. Main use is for ladies and slim watches.

Note: Battery Iilustrations are for identification only. Type number and manufacturers may vary. All batteries are high quality brands