I've read about calibrating batteries to optimize apparent battery life by fully cylcing them once or twice, removing/reinserting with them with the charger attached etc. I guess that some/all of this calibration occurs within the Treo and is not just conditioning of the battery itself but teaching the Treo how to interpret the voltage levels in terms of % capacity.

So what happens if you alternate between 2 batteries? Does the Treo get confused between them?