I have the Garmin S2 as well. Two things I have noticed with it:
1. make sure that the pins on the charger get a really good connection with the contact plates on the watch. Sometimes when there is some dirt or sun cream or whatever left on the back of the watch, the watch will not fully charge, no matter how long you leave it in the charger ... it normally helps to clean the contacts with a q-tip or a toothpick or something.
2. When the battery has been completely discharged, it takes a ridiculously long time to recharge. I usually leave mine in the charger over night, but if the watch died on me during the round because the battery ran completely out, I leave it on for at least 24 hours.
