I'm not sure what size battery I know it did work but when the battery died I took it out so it wouldn't corrode anything I can try to look and see for you.
Cool watch! I love watches and have a boatload. Batteries are expensive IF you buy them from a regular store. However, I just bought 5 of the kind you listed in a previous comment, 5 of the 364 SR621SW, and 10 of the 377/376 as they must be more common for a great price on Amazon. Wow, what do you know, the 377/366 says "REPLACES ALL: SR626W, SR626SW". You know I am now trying to tell of one is bigger than the other. I guess I now have another thing to add to the hundred thousand things I don't feel like listing. In all fairness, the Lidiots did me in on the last Samsung Galaxy S3 I listed. Not even remotely kidding!
I am so sorry I gave you that impression! Listia was great until the S3 auction and a couple of other things that happened. I simply got burned out. I'll be fine eventually. Separately, some other stuff is going on, which made everything worse than it needed to be, so a lot of this is definitely on me! Also I was trying to be funny and it would have been if you had been on here for a while, so I'm sorry about that. Thank you, because I learned something very important.