I have this wristwatch, which is also viewable in the online watch museum: Casio Wave Ceptor 3354 Wva - 430te Funkuhr Tough Solar Titanium Herren Armbanduhr. They have much better pictures than I have.

It is a solar watch that didn’t need any maintenance for many years. I needed a new watchstrap once. But since one or two years, every now and then the watch stopped. After a while, it started to work again; I just had to adjust the hands because it stopped in the middle. And after it started to move again, it didn’t display the correct analog time - while the digital time was already good. But that is possible with this clock - it’s even described in the manual under “Adjust analog time”.

This happened more often lately. It’s winter and cold (not good for a chemically based battery) and my sleeves usually cover the clock almost all the day. So it probably just ran out of power from the rechargeable battery - until it stopped. It couldn’t even go to save mode properly (moving the hands to 12:00). It just stopped.

The watch has a small solar panel, which is usually sufficient to charge the battery if enough sun light hits the surface during the day. And I had no problems at all for many years.

But now, after about 17 years in constant use, it’s time for a new battery it seems. Kudos to Casio, which made this easy repairable. The backplane uses 4 screws and then you are in. You replace the battery, there is a sign to use only the correct battery type - which I confirmed, I ordered the correct one: CTL1616. When putting in the new battery, the watch showed the same behavior as the before: It didn’t run, it was in some kind of emergency power save mode. The one indicator bottom left in the display was blinking, but no other signs were shown. If you short-circuit point AC with ground for two seconds - as noted on the sticker - it started to run. This behavior indicates, that the theory of a worn out battery after 17 years could be correct. I measured the voltage of the old battery - it showed about 2.4V. But so did the new battery. I guess, voltage on its own is just not a helpful indicator of the health of a rechargeable battery.

Anyway, I switched the battery now. Let’s see, how long this one lasts.

Here are some pictures:

watch - front side
watch - back side
inside of watch: sticker on the battery
inside of watch: sticker removed, battery visible
the new battery - looks like the correct type CTL1616 for casio
new battery left, old battery right: both are even from Panasonic
the old battery had an additional insulation which I reused