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Hi, i am very sure that the batterys are dead. APC recommends to change the batterys every 3 to 5 years. I'd change them every 3 years to be sure. Its very unlikely that your 6 year old packs are still fully functional. I had the same symptoms at a customers APC (3000VA) and the battery packs were dead. Try to locate the packs on ebay, can save quite a bunch of money (but beware of low quality packs).

http://stores.ebay.com/Gruber-Power-Services

I've used them multiple times and been very happy.

Malcolm

I have used them as well and been fairly happy. Beware that they will spam you to death (and responding to their mailings with removal requests continue to go unanswered). Brian