In my opinion it shouldn’t be necessary to change the battery on a solar powered watch for obvious reasons but searching on teh internet it seems that these watches are prone to battery failure. The battery is a Cobalt Titanium Lithium Rechargeable battery CTL1616 made by Panasonic and also SONY. Mine has already been replaced under waranty but when it failed again less than two years later Casio wanted more to change it than I can buy a new watch so I decided to do it myself.
First remove the strap by using a pin to compress the two pins in the usual way for any watch.
Now remove the four screws and take the back off
remove the rubber sheet to expose the battery cover, note this is not the battery but a sheet metal cover
Inser a needle into the cavity at the 12 o clock position and release the metal clip so the cover can be lifted and the battery slid out as shown in next photo
Slide the battery out. My battery had brown ooze at the join which doesn’t look healthy.
Put your new battery in observing polarity.
I found a link online for a comany that can supply them it is http://apc321.fatcow.com/store/page10.html or get there from http://www.ctl1616.com/ BTW I have no connection with either company, information only.
Update : – I fitted a non-rechargeable battery last October cost 20 pence on ebay (pack of 5 for £1) and it is still going strong with a “full charge” showing on the display after nearly a year of use
Summary: I wouldn’t bother with the expensive rechargeable CTL1616 when you can get this performance from a throwaway replacement cell.
Here is some data for the battery below for those that are interested