The LR52 / A640 is a mercury-free replacement for the RM640 / MR9 cell that was commonly used in cameras and carriage clocks. Mercury cells are now banned because of toxicity and environmental fears.
The LR52 / A640 cells produce 1.5 Volts, which is higher than the 1.35V produced by the original mercury cell. Most devices accommodate the small increase in voltage and function properly. Replacement For the following: PX640A, A640PX, RM640, MR9, EN640A, EPX640A, PC640A, LR52, 1126A, PX640, EPX640, V640PX, H-N, E640N, MR52, NR52, 1126MP