I got a 510 starter kit at the beginning of February and the pair has worked fine until last week. The batteries seem to need a longer charge to give the throat hit that they used to and the charge diminishes rapidly as they are used. At this point the batteries are around 80 days old and have been used heavily during that time. I went ahead and ordered two more new ones figuring they were at the end of their life. Is this performance normal for 510 batteries?