LR626 vs SR626SW
The LR626 and the SR626SW share one case, 6.8 mm across and 2.6 mm tall, so either drops into the same watch. The LR626 is 1.5 volt alkaline holding 12 to 18 mAh. The SR626SW, sold everywhere as the 377, is 1.55 volt silver oxide holding 25 to 28.
| LR626 | SR626SW | |
|---|---|---|
| Chemistry | Alkaline (Zn/MnO2) | Silver oxide (Ag2O) |
| Voltage | 1.5 V | 1.55 V |
| Diameter | 6.8 mm | 6.8 mm |
| Height | 2.6 mm | 2.6 mm |
| Capacity | 12-18 mAh | 25-28 mAh |
| Also sold as | AG4, LR66, L626, 177 | 377, SR66, V377, D377 |
Naming does its usual work of hiding a simple situation. The alkaline cell answers to LR626, AG4, LR66, L626, 177 and G4. The silver one is printed as SR626SW, 377, SR66, V377 or D377. Two products, one shared case, and 377 is the number battery counters use, since this is widely reckoned the most-fitted watch battery in the world.
What separates them shows up months later. The alkaline LR626 leaves 1.5 volts behind quickly and keeps sliding as it drains, so a quartz movement drifts before it stops. The silver-oxide 377 holds 1.55 volts almost to the end, then quits over a few days. Roughly double the capacity on top of that gives two to four years in a standard analog quartz watch, against about half as long from the alkaline.
Where each belongs follows from that. The LR626 is what fashion watches and cheap imported watches ship with, because it costs the factory a few cents, and it is fine in small LED gadgets that do not care about voltage. Anything you wear and rely on deserves the 377. One variant is worth knowing: the SR626W, sold as the 376, is the same case with a high-drain electrolyte for movements that run a light, alarm or chronograph motor.