I was doing some experimentation with wireless charging on the N900 and I noticed the back-up battery in the phone. This battery is designed to keep the RTC(real-time clock) running when the main battery is unplugged. My phone is quite old by now so I am pretty sure it is gone and the RTC is lost every time I swap out the main battery.

Based on my research it is most likely a rechargeable Lithium Iron Phosphate battery with nominal voltage of 3.2V but I may be completely off.

I searched on DigiKey but I can't seem to find any coincell battery that is even similar to that size.

Can someone shed some light on this?