Any battery experts in here?

Scott Malkinson wrote:
Ok, so I got my batteries set up and everything. Ended up pulling the console and puttiing them there with a custom console over it. But I'm not quite understanding how the charging works. I've got 2 155 amp hour agm batteries and the pro mariner 40 amp charger and a xantrax monitor.

I've got lights, tv and mini fridge all hooked up running on a 1000 watt inverter. All works fine, but the charging part is baffling me. From what I've learned, the charger charges in "fast charge" mode until it gets over 12.8 volts then kicks into "absorption" charge.

Yesterday I got it down to about 12.2-12.3 volts. I drive down the highway for over 2 hours before the absorption charge kicked in. About half hour after that kicked in I had to stop but left it running. The volts were 13. Started driving again, and not 5 minutes after driving the absorption charge stopped and volts dropped down to 12.5. Had to stop again, this time I turned the engine off. When I started it back up the volts shot up to 12.9 and the absorption charge kicked back in.

Got to my spot for the night about 10 minutes later and shut her off. Just fired it back up like an hour ago and volts went up to 12.9 again and absorption change kicked in. Then after it idled for a bit the volts dropped back down to 12.5.

Been idleiing for over an hour and the volts are at 12.6. There are times when I will drive just in town for an hour or so and the volts will actually be .1 lower than when I left, and the inverter isn't even on. Sorry to be so long winded, but I don't know **** about this and I'm confused as hell. Can any experts shine some light on this?

All those voltages look low for running off the engine charging system, unless you have an isolator (not a relay type separator in the circuit), and even then are low.

The charger and inverter would not normally be in the circuit at all, unless you are running the charger off the inverter off the engine alternator, which can add a lot of inefficiencies to all of it.

Most chargers, if you are running off the charger, do a pretty poor job of charging batteries to full, and if you are turning them on and off repeatedly, they can get very confused due to surface charge and loads.

Your readings all over the map are likely caused by surface charge being on and then going away over time, and/or the charger, if you are using it while driving, seeing surface charge and going directly to float.

I think we need to know how you are wired for charging, especially while driving, and the model numbers of the parts used, so we can try to understand what is going on.