So I updated my Atrix 2 with ICS about 10 days ago. Generally it's been working well. But on two separate occasions it seems the phone entered battery drain mode. Each time, the battery was at around two-thirds to three-quarters charge. Then in few hours of no use at all, it drained down to zero. The first time this happened it was during the night and the phone was sitting on the nightstand. The second time was this afternoon, while the phone was sitting unused in my pocket. Any thoughts on how to approach diagnosing the problem?