I have a Casio aviator G-Shock watch model G-1500-1ADR that I bought in 2012. It’s a solar powered watch which can stay many months in hibernation mode. Up till a year or two ago since I started rotating more watches and given less wrist time to it, the battery power indicator dropped from High charge to Medium charge. So I was wondering how long exactly would it take to recharge it back to High.
I experimented by putting it next to the window which has plenty of sunlight but my window is well tinted so there’s not much extra heat to potentially damage the battery. So I checked it daily and it took around a week or 7 days of sunlight to have it go back to High. So that’s an average of 70 hours of sunlight and if you keep wearing your watch it should stay that way. However if back to darkness, it took about a 2-3 weeks before it started going back to Medium. Another reason is probably that the battery is starting to get weak and does not hold its charge very long. That probably starts to happen after 5 years like mine. Hope that helps for those wondering about the same as I did.
For more accurate information, Casio has mentioned the actual charging time depends on the model of your watch. First, look at the back cover of your watch and find the three- or four-digit “module number”, then head on over here to find the standard charging time based on your module number.