Dual battery charging problems


Well-Known Member
Hey guys,

Sorry for the long post but best to try cover off on everything.

So previously I had a VSR wired and connected via Anderson plug to battery in tray, everything worked fine no issues.

I then turned off smart charge on my 2012 Ranger and installed a 50A fuse prior to second battery and off that a second run of 6BS cable to a second Anderson plug at end of tray to charge batteries in my camper.

I thought everything was fine as camper had dcdc charger and kept bats full, but it appeared it was flattening the battery in the tray, spoke to an auto elec and reckons the dcdc charger was pulling from battery in tray as it was on the same circuit so thought still connected.

I have since installed a second VSR between the dual batt and rear Anderson plug.

But now seems the second batt in tray isnt charging, multi meter showing 13.9v at Anderson plug in tray, but when i connect battery and driving all day with fridge plugged in the battery only at 12.4v so only barely holding on.

The camper was not connected during today's drive so all power should have charged the second batt in tray.

Anyone got any thoughts on how to fix?????


Well-Known Member
All I can suggest is tracing everything from front to back, as it sounds like there might be a continuity problem somewhere.
Check all your earth points as that is a common issue. I'm hoping you've run earth from the cranking battery, rather than relying on chassis earth.
You've said 13.9V on the plug without the second battery connected - what is the voltage when you plug the second battery in? If there's a substantial drop in voltage it could be your second battery is nearly dead and not accepting charge.
And make sure that you've actually got continuity for both leads from the plug to the second battery. Actually, check with plug connected that you have continuity from the second battery to the cranking battery. Anderson plug failures do occur, especially with the cheaper knock-offs.


Well-Known Member
You might also have a poor connection that will not support a load but still give you a reading on your multimeter.
I had that issue with a fuse that turned faulty on my fridge powerlead . It still showed me the correct voltage but as soon as it had the fridge load on it it dropped power


Well-Known Member
So your charging the aux battery off the starter then trying to charge the camper batteries off the aux if I read correctly. If so I would run the camper wiring directly off the starter battery so it has it's own set up independent from the vehicles aux.
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If your vehicle is a Ranger, do not run from battery negative under any circumstances or you will stuff your electronics, i run my spare batt of starter batt through a dcdc charger no probs but have gone into forscan and changed output to 13.3 volts, others may recommend a higher voltage
I would follow the above advice re leakage


Well-Known Member
Put your battery on a 240 volt charger.

The dc/dc was running all the time from aux battery, flattening it, which you cured with second vsr.

If the battery does not come back to life, it's fritzed.:cool:


Well-Known Member
Yeah I've currently got the battery connected to 240v charger to give it a good charge. I'm on the road and been off grid relying on solar and car to charge all batteries for the last 12 days, and in between I installed the second VSR so I'm hoping this will fix the issue but interested to see other replies as I have just started the GRR, time will tell I guess hahaha

Thanks for all the replies