LiPo will not charge at 1c anymore.

[gonpostal]

Well I had the max amp 6500 since beggining of this year, but now all of a sudden they only charge at 3 amps once its pass 80%. The other battery is fine its charges 6.5 amps all the way through. I'm using the 720i duo, always store at 60%, never fast charge them. Is it just that they get old and wear out?