LR1120 vs SR1120W
The LR1120 and SR1120 fill the same slim compartment: 11.6 mm across, listed at 2.1 mm tall for the alkaline and 2.05 for the silver. The LR1120 is 1.5 volt alkaline with 35 to 45 mAh. The SR1120 is 1.55 volt silver oxide with 45 to 55, sold as the 391 and the 381.
| LR1120 | SR1120W | |
|---|---|---|
| Chemistry | Alkaline (Zn/MnO2) | Silver oxide (Ag2O) |
| Voltage | 1.5 V | 1.55 V |
| Diameter | 11.6 mm | 11.6 mm |
| Height | 2.1 mm | 2.05 mm |
| Capacity | 35-45 mAh | 45-55 mAh |
| Also sold as | AG8, LR55, L1121, 191 | 391, SR55, V391, SR1120SW (381, low drain) |
This is the flat one in the 11.6 mm family, and that matters at the counter. The same diameter carries the LR1130 at 3.1 mm, the LR43 at 4.2 and the LR44 at 5.4, so height is the only thing that identifies the cell you need. Slim watches, calculators and small instruments are where the 2 mm version lives, and a taller cell in that recess stops the case back closing.
The codes then fan out. Alkaline: LR1120, AG8, LR55, L1121 and 191. Silver: SR1120W as the 391 for high drain, SR1120SW as the 381 for low drain, plus SR55 and V391 on other brands' packs. Long list, two batteries, one case that both of them share.
Silver oxide is why a watch counter stocks the 391 and 381 rather than the AG8. It holds 1.55 volts nearly flat until it empties, so a slim quartz movement keeps accurate time across the two to three years a 381 typically runs. Alkaline opens at 1.5 and sags from there, giving roughly half the watch life and a slow drift while it lasts. In a calculator or a novelty, the cheaper cell is no crime.