Lithium-Ion batteries (most probably the one in your device) sport a battery level meter, like an electronic “fuel gauge” or State Of Charge meter which is responsible for reading the amount of charge your device’s battery holds at a certain point. Windows Mobile uses the information from those readings to display remaining battery level on your device.
Many of you might have been in the situation (I know I have been) when your device notifies you of low battery but after soft reset, you power meter will show 20-30% left, or simply (and this happened to me several times) it will indicate a full charge when actual battery level is indicated at around 90%, but not 100%. You know you need to “recalibrate your battery” when anything like this happens.
Here’s the deal: even though it is not recommended to fully discharge Li-Ion batteries (as opposed to NiCd batteries), it is advised to do this around every 30-40th cycle (that is approximately 30-40 days or so for most people) in order to recalibrate the metering system on your battery. The principle is simple: you need to drain your battery completely so that the meter would acknowledge a close to 0% and start counting from there. Repeated everyday charging will get this slightly out of accuracy.
The bottom line: completely drain your battery around every 30-40th cycle and do a full recharge with the supplied wall charger while having the device powered off. Keep it charging until you see the fully charged LED notification. You’ve recalibrated your battery and contributed to its longer, healthier life.