Charge/Maintain two vehicles batteries with one charger

[lathamb]

Hi All, I'm about to relegate my 4Runner to roadtrip/offroading use only from a daily driver. I also have another car that I don't drive often. I'd like to maintain their batteries when not in use. My question is could I connect my ProNautic 1240 3-bank battery charger to both vehicles to maintain their batteries while not in use? I'd split the one ground from the charger and connect a negative branch to the negative of each battery (the two vehicles would share common negative/ground on the charger). I'd run individual positive leads to the respective batteries. My initial thought is that splitting the ground wouldn't cause issues since they all return to the same point. But I wanted to run that by those here who know much more than I do about battery charging.

Thanks,
Ben

 

[shade]

https://www.promariner.com/en/~/media/inriver/365008-38505.pdf

The charger wouldn't be able to detect each battery's state of charge, so the automated functions of the charger couldn't be used properly. You could connect the charger to each battery individually, let it bring each battery to 100% SOC, then connect both as you described and it could run in Auto Maintain mode, but again, you're asking it to use automatic functions in a way it isn't designed to work.

Others may have better advice, but I wouldn't do it. A second maintenance charger doesn't cost much, and would do a better job without complications.

 

[john61ct]

I don't like trusting even the best charger to be hooked up all the time.

If you're batteries are properly isolated from all loads, an overnight charge every few weeks is plenty to keep them healthy.

Yes you could keep loads running off a constant trickle / float current source but with an expensive deep cycle bank then I'd bypass that and use a cheap little batt to act as buffer while the system is in "hibernation mode" between true isolated storage and cycling.

In which case sure split the current who cares not being well maintained

 

[lathamb]

ok, probably best to just hit them with a charge once a month or so. Thanks for the input.

 

[john61ct]

Remember, that's only if well isolated from vampire loads.

Otherwise cycle frequency needs to be determined using a coulomb counter or battery life will be reduced a lot, lead really needs to sit at 100%, not even 99.5% for optimal longevity.

 

[john61ct]

If we're just talking cheap Starter batts, never mind, they should be getting replaced pretty frequently anyway.

 

[luthj]

I like a 100-200mA float only charger for that kind of thing. Cheap enough, and will easily keep a battery topped up in storage.

 

[rayra]

You can do both. But car collectors use affordable tenders, one for each vehicle / battery.
Your other option is dismounting the batteries and set up some sort of charging station where their maintenance can be more convenient. But that will zero all your vehicle computers' learned engine data.

examples - depends on your battery chemistry, too.

Battery Tender 800 Weatherproof 12v Battery Charger - 022-0150-DL-WH - California Car Cover Company

All Battery Tender 022-0150-DL-WH weatherproof battery chargers are designed to fully charge and maintain a wide range of styles of lead acid batteries in ways that avoid the potential damaging effects that can be caused by most trickle chargers.

www.calcarcover.com

Battery Tender 2-Bank Battery Charger 022-0165-DL-WH

Never be without power again! The Battery Tender 2-Bank Battery Charger 022-0165-DL-WH is the best way to safely recharge a wide range batteries. California Car Cover Co. has got you covered

www.calcarcover.com

Another easy solution is a solar panel kit with charge controller.

I'm running dual batteries under-hood. Combined with a solenoid while the vehicle is running / charging, separated when the key is off. My rooftop solar is backfeeding my Aux battery thru the solar PWC controller. So my Aux is always getting topped off / 'maintained' by the solar. It's always a lot closer to 13V than my Starter battery is, with the factory parasitic drains on it. Even now with my high output alternator.