AGM battery high self discharge?

[micky 32]

Hi all. I have one of those start/stop energy recuperation cars coming on 6 years. I think the battery is usually kept at a SOC of around 80% charged for most part.

Over the last few years it's cranking isn't as strong as it used to be compared to when new, but expected as the battery ages. It still starts at -7 degrees C.

I left the car at the airport for a week. I have one of those BM2 Battery monitors on the car. It was a 2 hour drive and the alternator was charging the battery full whack for the 2 hours at approx 14.4v. Here are the results after sitting for 7 days:

Day 0 : 12.71V

Day 1 : 12.59V

Day 2 :12.50V

Day 3 :12.49V

Day 4 : 12.45V

Day 5 : 12.44V

Day 6 : 12.42V

The car started ok but was sluggish. Is this a high discharge rate or just due to normal parasitic drain from the car? Is the battery toast?

[organic farmer]

... Is the battery toast?

I dont think it is toast yet.

It still has enough power available to start the ICE, so your good.

But it is aging.

When parked at home, do you keep it plugged in?

To my understanding what kills batteries is cycling.

[bcroe]

One thing often ignored in a starter, is the brushes worn to
end of life. A new set are regular maintenance here. But,
perhaps that starting arrangement does not use a brush motor.
Bruce Roe

[micky 32]

I put a conductance tester on it today. The battery is rated at 680 A (EN/CCA). The results were 350 A (EN/CCA) 26% SOH with the message “ REPLACE”. I’m sure 350 A is still enough to start a 2.0L diesel engine for another while i’m sure.