Can you charge two batteries with one charger?

[The motor guy]

The more stuff I have to unhook, the less likely I'll bother doing this. I'm pretty sure the batteries in my diesel truck monitor voltage on one battery and charge the other and the voltage from that battery being charged, carries over to the other battery. I'd like to hook up a noco 5amp battery charger/tinder every so often to top the batteries off. Can I just hook a charger up to one battery and let it charge both of them as I described without unhooking the battery cables and isolate each battery? Just to clarify these are two 12v batteries hooked in parallel.

 

[nwjones18]

I don’t see why you couldn’t

 

[Chris142]

Yes. That is how the alternator charges them anyway.

 

[The motor guy]

Yes. That is how the alternator charges them anyway.

I forgot which one it charges.

 

[ripcord]

The batteries are connected in parallel so connecting the charger up to one battery charges them both at the same time. If you have a volt meter you can see it for yourself. With the charger connected to one battery and charging, measure the voltage on both batteries. You should see them be within a half a volt of each other. Any minor difference in voltage will be due to the resistance of the wires.

 

[Jetronic]

they are seen as 1 big battery by the charging system.

 

[Patrick0525]

Electrical it will work and charge, but I asked the BatteryMinder customer service for two batteries in two cars and he said it is not ideal unless it is bench top application and both batteries were fully charged before going into to the final float voltage stage. He said for ideal desulphantion maintenance purchase two chargers.

 

[eljefino]

The more charged battery will put up more resistance so the weaker battery will get more current until it too considers itself fully charged. It "should" even out. This is why you should buy two batteries of the same brand at the same time.

Patrick is right, if you want to bring each one up to their fullest conceivable strengths through a desulphation mode or whatever it's best done individually. If you're just throwing a trickle charger on because you haven't run it in a while you can do both at the same time.

 

[Jetronic]

Electrical it will work and charge, but I asked the BatteryMinder customer service for two batteries in two cars and he said it is not ideal unless it is bench top application and both batteries were fully charged before going into to the final float voltage stage. He said for ideal desulphantion maintenance purchase two chargers.

but then you would have to disconnect the batteries from each other aswell, that's not always practical under the hood. it's ideal on a bench as batteryminder said.

 

[paulswagelock]

As long as both batteries are healthy, it will work fine.

 

[Patrick0525]

The more charged battery will put up more resistance so the weaker battery will get more current until it too considers itself fully charged. It "should" even out. This is why you should buy two batteries of the same brand at the same time.

Patrick is right, if you want to bring each one up to their fullest conceivable strengths through a desulphation mode or whatever it's best done individually. If you're just throwing a trickle charger on because you haven't run it in a while you can do both at the same time.

Agree. Ideally both batteries should be charged separately since bulk and adsorption states are different and require different voltage/current charge duration times. Once completed the float voltage stage could be connected and charged together. The assumption is that both batteries are homogeneous flooded cells. An AGM and a flooded cell configuration would require two chargers to be optimal.

 

[The motor guy]

My noco charger has a repair mode. Is that the same as a desulphation mode?

 

[eljefino]

My noco charger has a repair mode. Is that the same as a desulphation mode?

Did It come with a manual? Read it and find out!

 

[puellarum]

I do this with a trickle charger. I hook it up to the auxiliary battery, but there really is no auxiliary battery because the batteries are hooked together and function as one big battery. Also, my experience is that if you leave a trickle charger hooked up to car batteries, they tend to last many years. Way longer than they otherwise would last.

 

[UncleDave]

Yes, BUT if you are using a modern smart charger you need to make sure the combined AH is within the range of its logic or other will likely stop charging and indicate a fault.

This isnt likely to rear its head if the batteries are charged up, but if charging from a low SOC it will rear its head.

Some charger companies from and center this info.
Others bury it in their manual.

 

[The motor guy]

I gave it a whirl. My 5 amp noco charger topped up both 750cca batteries in about 7hrs, battery voltage was steady on both batteries. The batteries were down to 12.2v a few days ago after not driving for about a month because the heater doesn't work and it's been too cold. I did drive it for about an hour earlier in the week, so not sure how much that topped them off as I never did check after.

 

[The motor guy]

I do this with a trickle charger. I hook it up to the auxiliary battery, but there really is no auxiliary battery because the batteries are hooked together and function as one big battery. Also, my experience is that if you leave a trickle charger hooked up to car batteries, they tend to last many years. Way longer than they otherwise would last.

I don't doubt it. Had a friend that was good about maintaining water level in his battery and keeping them charged. He said it was 5 years old and still going. Lol down here in our tx heat

 

[meep]

My noco charger has a repair mode. Is that the same as a desulphation mode?

Having built desulphators, the stuff available for common use isnt effective to any amount able degree. The NOCO I had would use a higher charging voltage in some strategy it had. I did appreciate its ability to be more aggressive in this mode, but otherwise NOCO is pretty conservative in its methods. Use it if you just flatlined it leaving the lights on overnight. If the battery wasnt mistreated and is gradually weakening, consider it more of a “Hail Mary” mode - if you need it and it makes a difference, the battery has limited time left

 

[The motor guy]

Having built desulphators, the stuff available for common use isnt effective to any amount able degree. The NOCO I had would use a higher charging voltage in some strategy it had. I did appreciate its ability to be more aggressive in this mode, but otherwise NOCO is pretty conservative in its methods. Use it if you just flatlined it leaving the lights on overnight. If the battery wasnt mistreated and is gradually weakening, consider it more of a “Hail Mary” mode - if you need it and it makes a difference, the battery has limited time left

I brought one of my boat batteries back from being dead about a year ago. I don't think it stayed dead for more than a week or so. I think I left something on and it ran down. The starter would just click. Turned the battery switch to the other battery and it started fine, but it took a good 12hrs for the on board marine charger to bring it back up to a full charge when I got home.

 

[The motor guy]

Can I put one charger on each battery to make it twice as fast? I have like 3 of these noco 5 amp chargers that I keep on various things at all times.