What if you keep the charger attached to your palm and go to Opie? What happens?

The battery icon turns green and shows the "charging" animation. But as soon as I remove the charger cable, it turns back to blue and displays less than 100%. This time it showed 68%, even though it was charging for almost 24 hours.

When I reboot and go to PalmOS, it shows about 4 pixels less than a full battery (probably around 90%).

How old is your battery? Battery driver measure voltage through my experimental equation. But max. voltage is hard defined as 4,1V (full power of Li-Ion or Li-Pol cells). 88% in Opie indicates decrease voltage after unplugging charger -> old battery. Measurement in PalmOS isn't precise, only roughly.