Just seen your post OP:
Have seen a solar G Shock for £67. If I left it in a drawer and it went totally flat what would you do then?
Is it best then to leave it on a window sill?
I wear a watch about 4 times a year. Not often but it’s a pain when it’s not there.
Wearing it just four times a year should be fine. Despite the variable performance of other solar powered devices, these watches are incredibly efficient and don’t need that much light to function and hold their ‘charge’ for ages. They will also draw power from artificial light as well as sunlight.
Might be worth checking what the power reserve is on the Casio. I’m guessing it’ll probably be about 6 months like my watch. Doesn’t necessarily need to be on a window sill in full sunlight. Best stored out of a drawer though, preferably in relatively bright room I would suggest.
In answer to your question about what happens if in the unlikely event the watch goes flat, if it has radio controlled timekeeping (see my earlier post on this) as well as solar power, as it charges up again it will reset itself with the correct time and date.