Not the same phone as yours, but I had a similar problem on my Motorola A910... was advised to give it a good 8 hour charge, then put it on charge every night... this does appear to have solved the problem. The reason was given that there is one quite large screen on the phone, coupled with it constantly have BT and Wi-Fi on, the battery is rather intensely used... so maintaining a full charge avoids any oddities like shutting off randomly, and freezing.
Probably way off the mark... but worth a bash.