I picked up a nano a couple of weeks ago exclusively for use in my car via the aux in port. On a full charge the nano gave me a low battery warning after no more than 45 minutes. I did have the volume at 100% to get sufficient input for the radio. Might the 100% volume be the culprit in draining the battery so quickly? I've done a factory reset and battery calibration (full charge / full drain / full recharge) with "minimal at best" results.