My son really loved this watch and wore it all the time. The problem is that during the winter the watch does not get enough sun light and sometimes lost all power. Even after we charge to medium it will be out of power in a few hours. I took it out to the full sun for a whole day when my son was in school. The power was full in the end. But the next day the power became medium again.
Update: we bought this watch for my son in August 2012. Now the battery is not working any longer. Even under the full sun for two days, the charge is just to medium and it runs out of juice in a day. We sent it back to the repair shop to replace the battery. It is under the warranty. We just received the notice as such: flat charge: 0 parts: 20 labor 0 sub total including tax 21.65 shipping and handling 9.95 please pay this amount: $31.60 Thus, it costs more than half of a new watch to get the battery replaced. March 22, 2013.