AGM 129Ah battery - charging while driving and also battery usage meter

Hi,

I have an AGM 120Ah battery.

1. I have it linked via an Anderson plug to my car battery while driving (Holden Commodore 2018)

Is it likely to overcharge the AGM battery?

I have been told it may not actually charge the battery well?

2. Is there a meter that helps me see how many Ah I am using off my AGM battery?

Thanks

Ken

Hi Ken to my limited knowledge I believe most car manufactured after 2006 have smart alternators, I would say yours does. This means when the alternator detects the starting battery is fully charged it shuts down most of its capacity.
to charge an auxiliary battery you should have a dc to dc charger. As for detecting amps you need a good volt meter and knowledge how to use one or a coulomb meter.