LR621 vs SR621SW
The LR621 and SR621SW are the same tiny cell size, 6.8 mm across and 2.1 mm tall. The LR621 is 1.5 volt alkaline with 13 to 18 mAh. The SR621SW, known everywhere as the 364, is 1.55 volt silver oxide with 18 to 23 mAh and a discharge curve that stays flat.
| LR621 | SR621SW | |
|---|---|---|
| Chemistry | Alkaline (Zn/MnO2) | Silver oxide (Ag2O) |
| Voltage | 1.5 V | 1.55 V |
| Diameter | 6.8 mm | 6.8 mm |
| Height | 2.1 mm | 2.1 mm |
| Capacity | 13-18 mAh | 18-23 mAh |
| Also sold as | AG1, LR60, L621, 164 | 364, SR60, V364, D364 |
Small analog watches are almost the whole story at this size. Ladies' watches, kids' watches and mini quartz calibers take it, and the 364 is one of the best-selling watch batteries on earth. The alkaline AG1 mostly arrives as the factory cell inside an inexpensive watch, or inside a miniature LED light where nothing about the voltage matters.
The numbers people actually notice are runtimes. An AG1 gives a basic analog watch roughly 8 to 14 months, with the timekeeping drifting along the way as 1.5 volts falls off. A 364 in that same watch usually runs two to three years and keeps accurate time throughout, because silver oxide holds 1.55 volts until it is nearly empty and then stops quite suddenly.
The alkaline answers to LR621, AG1, LR60, L621, 164 and G1. The silver is SR621SW, 364, SR60, V364 or D364, with SR621W, the 363, as the high-drain version for movements running an alarm, light or chronograph hands. Battery counters barely stock the alkaline in this size, since nearly everyone replacing a 6.8 by 2.1 mm cell is servicing a watch.