Starter battery question

rob_gendreau · 09-07-2019, 02:52 PM

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?

arctictraveller · 09-07-2019, 09:15 PM

A fully charged AGM should be around 12.8 or 12.9v, and it should hold near that voltage for several days. 12.3v is considered close to fully discharged. 5 years is a pretty good life span, 3 to 5 years is common, so it's probably due for replacement.

1der · 09-08-2019, 04:46 AM

Does the battery ever get a proper charging via a plugged in 3 or 4 stage charger of ii it only getting charged via the alternator? Same w your house battery?

rob_gendreau · 09-08-2019, 08:51 AM

Quote:

Originally Posted by 1der

Does the battery ever get a proper charging via a plugged in 3 or 4 stage charger of ii it only getting charged via the alternator? Same w your house battery?

At most I could get it to 12.58 via my plug-in AC Schumacher charger (yes, a multistage charge with desulfation).

As I noted the alternator works fine; it puts out enough current to supply 35amps to my house LiFePO4 batteries.

The battery has a low internal resistance, and the CCA's remain high (say 900 vs the original 950), but I fear that the lower voltage means a lower capacity. Is that possible? In other words to get a lot of amps but still have low capacity, which could affect the number of starts?

rob_gendreau · 09-09-2019, 01:52 PM

Update: turns out that with the battery disconnected it self-discharged over .15v over just say 30 hours, and that was a couple days after last good charge (so not just a surface charge wearing off). So kinda toast.

And BTW a source of my phantom load turned out to be my Scangauge. Not every single time, but it seemed to use around 100mA with ignition off.