I have two anker batteries and I tried charging my watch for several minutes with both of them and didn't have any problems. I did see another thread on here where someone else said that it wasn't working with his batteries, so there may be some that have problems.
That said, though, I really haven't had any problems with battery life on the watch... for the first couple of days I carried around a spare battery and the charging cable with me in case I needed it, but I never did. Now, after having used the watch for two weeks I don't worry about it anymore. I think the lowest it's ever been when I plug it in at night is 35 or 40% and often it's above 50%.