This seems to be an obvious issue with the Thunderbolt! I have had my Thunderbolt for about 18 months and have had 3 replacements. My phone started randomly restarting its self a couple of months ago and each day it is getting progressively more frequent, now it sometimes just shuts down and doesn’t restart. I also experience the battery issues with the shutdowns and restarts.  I will have 75% battery, and then my phone will restart and only have 6% battery. Or it will shut off and I’ll turn it back on and it will have had a 20%-30% battery loss but if I try to use the phone at all it will say 0% battery and turn off. It has stopped giving me any battery warnings.  It is really frustrating to have a phone that turns off every 5 minutes! HTC and Verizon need to fix this issue!