Starter battery question

[rob_gendreau]

I've got a five year old Odyssey Extreme starter battery; it's an AGM 950CCA, group 65. In an E250 gas engine van.

It seems kind of weak; first noticed starting in about 25 degrees F back in May. I can only seem to get it up to about 12.55v, either through long driving or once on a charger. I've tested it with an auto parts tester and my own cheapo HF unit; shows 900-1000 CCA, about 12.58v max, 2.5 m Ohm resistance. But just this last week I drove a couple hours and by next morning it's down to 12.31. I have a phantom draw somewhere (aargh), but even still, with it disconnected it will still drop about that far in a few days. I even had my auto mechanic test it when I was getting some work done and the numbers were in line what I got above.

So I'm wondering whether it ought to be replaced. I don't seem to be having a problem with the alternator; it happily charged my new house batteries at the max I'd set at 35 amps. Connections seem fine as well. I'm not sure about the internal resistance numbers, but the CCA seems OK. Just that the voltage seems to drop below what I'd expect for an AGM this old. Or maybe I'm just worrying over nothing.

Any thoughts?