Winter trickle charging parallel batteries

[JoeInPA]

I just removed the parallel batteries from our TT and brought them into my workshop for the winter. I want to use a trickle charger for the next 5-6 months. Can I leave the parallel cables connected between them, and just connect the charger to one battery? It seems like this should be fine, since there's no difference I can think of between doing that, and what happens when the batteries are installed on the TT and charging off the TT inverter when on shore power, or when connected to the TV 7-pin cable.

[cboss]

Originally Posted by JoeInPA

Can I leave the parallel cables connected between them, and just connect the charger to one battery? It seems like this should be fine, since there's no difference I can think of between doing that, and what happens when the batteries are installed on the TT and charging off the TT inverter when on shore power, or when connected to the TV 7-pin cable.

Exactly. Should be no problem.

[SeaDog]

I use a battery maintainer on my rig and boat (both have dual batteries) with no problems.

[61Tele]

Yes but no need to. Just disconnect them, and make sure they're fully charged and topped off. They'll be fine. No need for having them on a maintainer for 5-6 months.

[TitanMike]

Originally Posted by 61Tele

Yes but no need to. Just disconnect them, and make sure they're fully charged and topped off. They'll be fine. No need for having them on a maintainer for 5-6 months.

True, a maintainer isn't required, but using one is actually better for the batteries. Lead Acid batteries still self discharge, no matter how good a brand. During the time they sit at any level of discharge SOME sulfation occurs. Even if it isn't much it does occur and becomes cumulative.

If one wants the absolute maximum life possible out of a battery, storing with a maintainer connected (and plugged in) during storage is the absolute best way to achieve that.

It's kind of a choice between "The Best Way" and "Good Enough".

[SailorSam20500]

Bringing your batteries into your workshop has probably increased the need for a trickle charger. The warmer the batteries are the faster they self discharge. A recommended temp for L/A battery storage by the US Army COE is 5F.

[sasch]

Great question post - I am getting ready to set batteries up for the winter by using the battery disconnect switch then connecting a trickle charger/maintainer for the winter months. I've had good success with other batteries by using a trickle charger but not yet tried with a parallel condition so your post and others answers were helpful. Thank you all!

[camaraderie]

Originally Posted by 61Tele

Yes but no need to. Just disconnect them, and make sure they're fully charged and topped off. They'll be fine. No need for having them on a maintainer for 5-6 months.

Inside at room temps they will lose 10% a month

Leave em outside and they'll be fine with only a 1 or 2 percent loss

[TitanMike]

Originally Posted by sasch

Great question post - I am getting ready to set batteries up for the winter by using the battery disconnect switch then connecting a trickle charger/maintainer for the winter months. I've had good success with other batteries by using a trickle charger but not yet tried with a parallel condition so your post and others answers were helpful. Thank you all!

Batteries connected in parallel are just one larger battery as far as a charger is concerned. According to "Battery University" lead acid batteries can self discharge up to 3% per month so a maintainer large enough to " maintain" is recommended. Some small "Wall Wart" maintainers may be fine for small batteries but fall short on larger ones, especially two in parallel.

[pmsherman]

Originally Posted by JoeInPA

I just removed the parallel batteries from our TT and brought them into my workshop for the winter. I want to use a trickle charger for the next 5-6 months. Can I leave the parallel cables connected between them, and just connect the charger to one battery? It seems like this should be fine, since there's no difference I can think of between doing that, and what happens when the batteries are installed on the TT and charging off the TT inverter when on shore power, or when connected to the TV 7-pin cable.

No issue keeping them hooked up to a battery maintainer. Hooking the maintainer up to a single battery isn't the best way to keep them charged. That hookup will maintain the two batteries at slightly different rates which isn't good for them. A better approach is to keep them hooked up with the parallel cables, making them a single larger battery. The maintainer is then connected to the plus terminal on one battery and the minus terminal on the other battery. If you follow the cable lengths, you'll see than the cable lengths to both batteries will be the same length with this arrangement.

If the maintainer is attached to a single battery, the other battery has longer cable lengths to it which should have a small effect on the charge delivered to the second battery.


Phil

[TitanMike]

Originally Posted by pmsherman

No issue keeping them hooked up to a battery maintainer. Hooking the maintainer up to a single battery isn't the best way to keep them charged. That hookup will maintain the two batteries at slightly different rates which isn't good for them. A better approach is to keep them hooked up with the parallel cables, making them a single larger battery. The maintainer is then connected to the plus terminal on one battery and the minus terminal on the other battery. If you follow the cable lengths, you'll see than the cable lengths to both batteries will be the same length with this arrangement.

If the maintainer is attached to a single battery, the other battery has longer cable lengths to it which should have a small effect on the charge delivered to the second battery.


Phil

What you say is correct for high charging currents but at the average <5 amp maintainer current voltage drop will be negligible. Actually almost non existant for practical purposes.

[ve6kjm]

I have 2 - 75aH AGM batteries on my TT, and I don't remove them, I just unplug the trailer from shore power and connect my battery tender/maintainer to the the battery terminal of Solar Panel controller. have been doing this for years on both TT & 5th wheel (Has 2 - 125aH AGM). Never lost a battery yet and they been in service over 10 years.

[JoeInPA]

I went with this for the winter, and it seemed to work fine.

https://www.harborfreight.com/4-amp-...ner-63350.html

[Half Ton Heavy]

You might get slightly better life/performance if you hook the load across both batteries instead of just one. It will force them to share better.

[Chuck_S]

Coming up six months late to this party... But if the batteries are wired like the photo they're wired wrong.

Wrong (yours):


Correct (Yeah the difference is subtle):


And, no, the sky is not falling but it's best to be correct.

-- Chuck

[JoeInPA]

The photo was before I removed everything from the travel trailer. But I probably did connect things less than optimally on my work bench. I just had the batteries connected + to + and - to - with the same single red and black cables from the trailer. I connected the + and - charger/maintainer device cables to the + and - terminals of one of the batteries. I tried it with the charger's + cable on one battery and the - cable to the other battery for a bit, but the readout did not look right, so I put it back. Every couple weeks, I just moved the charger cables to the other battery. Display readout was showing 13V consistently on both batteries all winter, so I think (hope) everything was fine. Now that the batteries are back in the TT, I have them on the shore power charging.