Why does my Milestone Droid erroneously report a drained battery once every few weeks? Every so often, my phone (Motorola Milestone, firmware 2.1-update1) decides that the battery is almost drained and that I have to turn the phone off.  This may happen just a few hours after charging it, and a subsequent restart confirms that yes, the battery does still have a charge, still at 70-80% capacity.

This tends to happen every few weeks, and it's been happening basically ever since I bought the phone a few months ago, so I'm pretty sure it's not a charge memory issue, especially when combined with the fact that the problem is intermittent and very infrequent.

Does anyone know why this might happen, and what I could do to fix it?
Some custom recovery images have a command to clear the battery cache, this has fixed similar problems on different phones for me.