Paul,
I just buy a new one each year, usually at Brodak's, then use the older ones to fly on practice days and the newest on contest or club meeting day, I have 4 in my box right now , oldest was bought in june 2008
I put a label on mine with the purchase date and my name, when they are quick to die, or will not take a charge i send them to the battery recycle bin at work
Probably a good idea to check on having rebuilt ,but I have never done it