HSG80 cache battery will not charge

[SC04KJ]

I have an HSG80 dual controller SANS in a redundant configuration. One of the cache batteries failed and I tried to replace it. The new battery will not fully charge within the 10 hour expected time limit. I tried a second new battery and it also will not charge, I then tried the new cache batteries in my test SANS and they both charged fine in the test SANS. So... My question is, If the batteries are good but still will not charge, what would be the suspected bad component in my production SANS? Thanks.