Hey all. The charge provided by the solar cells on the watch only really extend the life of the battery. The total run time of a battery depends on how the watch is used... backlight
requirements etc. The battery will be depleted and need to be replaced.
Here is a site that has good instructions
on how to change the battery in your G-Shock watch.
If you want to ensure you still have a the same water resistance
rating, I do suggest that you take it to a watch guy to have it replaced
for you. They clean switch contacts also and you keep water resistance rating. Good Luck and vote this as a "FixYa". Cheers