Well, we can always pipe STDERR to a file in /tmp/, then read that file. The only issue would be determining -real- errors from comments or errors not caused by the OC process(say a slightly corrupted video file etc.)
Actually, this is something of a myth. Rebooting resets the internal battery percentage calculation, which is then based solely on the battery voltage. This means that -- depending -- a reboot can cause relatively unpredictable results in the battery % value. Sometimes it will go down 10%, sometimes up... But 10 reboots in under an hour won't drain your battery completely, no matter how much a single reboot "drained". It -will- take some power though, but considering that you should be able to run fully loaded for 3-6hrs(depending on condition of the battery), it shouldn't be -that- much of a problem. Charging it during the test probably wouldn't hurt -too- much, and charging it before the test would also be a good idea.