I have a Casio Pro-trek PRG-90 Casio number is 2894. The watch is a solar powered watch, the reason I bought one was the idea of never needing to replace the battery had appealed to me. I've owned this watch for little over 4 years now and on the display it says "open" all functions of the watch has stopped. From my research the battery that retains the solar charge needs replacing. Irony is my other watch which is not solar powered still has its original battery and it is almost 5 years old!
No, I don't use the functions of my watch very often at all, I've touched the function buttons no more than 10 times during the time I've owned it.
So much for solar powered watches, bring me to the point of why?
Edit: After conferring with Casio, it is not the battery that requires replacement the "open" that is displayed is the watch detecting the backing plate has become opened. So I removed the backing plate, fiddled around with springs which complete the circuit with the backing plate, put everything back together and the watch is now functioning normally.