Hi everyone. Old member that has been on a long hiatus. Our day has come and we are now retired so I am fortifying the camper with extra power in the form of solar panels and batteries.I removed the Onan 2500 genset to install 2 6 volt batteries instead and added 400w solar panels on the roof. Batteries added are 2 Trojan T-105 RE batteries. I am considering running them along with 2 12 volt flooded deep cycle batteries in the OEM battery compartment. I purchased a charge controller along with the solar panels.The advice seems pretty divided on mixing batteries like this to form a unified battery bank charged by solar, engine alternator and 110 plug in. Note the 2 6 volt batteries are a good 8 feet away from the 12v batteries and solar charge controller.Not wishing to start a debate. Researching this I see many opinions regarding mixing different sized batteries in parallel. Anyone else have experience with this?

I wouldn't mix the batteries, but you could get two charge controllers and have two solar systems (many options here), or you could set up a marine battery switch so you could charge the Trojans and then when they are full, use the switch to charge the other batteries.

We camp alot off-grid using our batteries. Can do alot of things every day but by 8AM the next morning will want to recharge my batteries from their 50% charge state back up to the 90% charge state so we can do all of this all over again for the next day/night battery run.I haven't gone with solar yet but having my small 2KW generator around is a must have item for me. It works rain or shine and even on cloudy days for sure haha...With my setup and small area for solar panels I probably would only get a solar benefit of reducing my use of the small generator down to perhaps one hour a day verses the three hour run to get past the 50AMPS plus DC charging current demand of the batteries for the initial re-charge procedure. Then the solar panels could continue giving me the batteries charge demand of 6-8AMPs for remaining of high sun for the day perhaps...Not having a generator around would not be a good idea in my setup. Got to have a good PLAN B here...My new battery bank I am working on will be two groups of 6VDC Trojans GC2 batteries in series to give me around 480AHs capacity... I too have not had good luck charging different batteries at the same time using the same charger. What I do here is use the on-board converter/charger PD9260C 60AMP Smart mode unit for the main battery group and then use my portable B&D VEC1093DBD 40AMP smart mode charger for the external batteries I sometimes carry with me for backup. Roy Ken

dms1 wrote:I wouldn't mix the batteries,I wouldn't either.And I definitely wouldn't do without a generator.I'll be interested to see how this turns out.

I also wouldn't mix sizes and ages of batteriesI worked for a large inverter manufacturer for 8 years, which is one of the companies that got swallowed up by Xantrex. We ALWAYS recommended not mixing battery types, size and ages in a battery bank.

Well, if you didn't want to start a debate you shouldn't have posted, because this subject inevitably starts a debate.Ideally, you should not mix battery sizes, at least on a long term basis.Electrically it will work fine but over a period of time the differences between the batteries could cause problems. Weak batteries will kill good batteries for sure.I've been using different battery banks in parallel for years. One bank in my truck and another in the trailer. When I'm drawing power for the camper they are connected. When I get home I disconnect from the trailer and park the camper in the barn, so they are never connected long-term.

Combining battery sizes in parallel. | Good Sam Community

ticki2
Explorer
Dec 08, 2016
ScottG wrote:
This is done every day in the commercial world. I would separate them into two banks and charge them together but use and store them separately. For best efficiency, I would only connect them all together when charging.

I am certainly not a 12v guru but it seems to me that any of us charging from the trucks alternator are doing this regularly . The truck and house batteries are almost never the same size or type battery .
work2much
Explorer
Dec 08, 2016
towpro wrote:
why not just put another 2 Trojan T-105 RE's in the OEM battery location?

Not big enough.
work2much
Explorer
Dec 08, 2016
ticki2 wrote:
ScottG wrote:
This is done every day in the commercial world. I would separate them into two banks and charge them together but use and store them separately. For best efficiency, I would only connect them all together when charging.

I am certainly not a 12v guru but it seems to me that any of us charging from the trucks alternator are doing this regularly . The truck and house batteries are almost never the same size or type battery .

This is a common argument that does make sense to me.
work2much
Explorer
Dec 08, 2016
Thanks everyone for the responses. I have read a few times if the batteries are the same type i.e.: wet flooded that putting them in parallel is ok even with different amp hour ratings. I have also heard many responses like here that it isn't a good idea.

I am starting to think about keeping both battery sets but only hooking the solar up to the trojans and using it as our primary power source. The 2 12 volt batteries would charge when we drive and serve as a back up that would be available when/if the trojans get down to 50%

I can install a switch that allows battery A, battery B or both so they wouldn't connected to each other but both available for power. This would also give me the ability to play around using both and go back to one easily.

I think this will work fine for us. We don't use much power the way we camp. No air, microwave, forced air furnace, big tv's etc.
work2much
Explorer
Dec 08, 2016
dms1 wrote:
I you could set up a marine battery switch so you could charge the Trojans and then when they are full, use the switch to charge the other batteries.

Interesting idea.
towpro
Explorer
Dec 09, 2016
work2much wrote:
towpro wrote:
why not just put another 2 Trojan T-105 RE's in the OEM battery location?

Not big enough.

Not sure how big your battery case is.
Mike put 2 in his Wolf Creek, which have enough space for two 24/27 series 12v batteries. but he had to lay them on side.
http://truckcamperadventure.com/2012/05/lifeline-agm-battery-upgrade/
covered_wagon
Explorer
Dec 09, 2016
Unlike paralleled batteries equals one being overcharged and the other being undercharged, with both resulting in eventual damage and reduced capacity.
work2much
Explorer
Dec 09, 2016
towpro wrote:
work2much wrote:
towpro wrote:
why not just put another 2 Trojan T-105 RE's in the OEM battery location?

Not big enough.

Not sure how big your battery case is.
Mike put 2 in his Wolf Creek, which have enough space for two 24/27 series 12v batteries. but he had to lay them on side.
http://truckcamperadventure.com/2012/05/lifeline-agm-battery-upgrade/

The trojans are not sealed batteries and can't be laid on their side. From what I understand mixing battery types is a definite no-no.

Looks like a perfect set up for your camper though!
pigman1
Explorer
Dec 09, 2016
ticki2 wrote:
ScottG wrote:
This is done every day in the commercial world. I would separate them into two banks and charge them together but use and store them separately. For best efficiency, I would only connect them all together when charging.

I am certainly not a 12v guru but it seems to me that any of us charging from the trucks alternator are doing this regularly . The truck and house batteries are almost never the same size or type battery .

Yep. When I ran my RV setup they were probably run in parallel (for charging and use) about 60-70% of the time. When you try to actually get into the technical specifics of why the "everybody knows" guidance is what it is, the information is somewhat fuzzy and the "damage" or "inefficiencies" you'll see tends to come from conjecture rather than actual testing or experience. Rather than depending on "dumb luck", decide what you want to do, do as much actual research as you can on the specifics, and then make your decision. Your results may occasionally not work out the way you want, but my experience says that you'll have more way winners than losers.
woodhog
Explorer
Dec 10, 2016
"I am certainly not a 12v guru but it seems to me that any of us charging from the trucks alternator are doing this regularly . The truck and house batteries are almost never the same size or type battery ."

This never got answered, very relevant to most of our TC's, does this not matter because they are only all in parallel during charging, what about the trucks that have 12 volts at all times at the trailer connection.

This mixes, 6 volt Deep cycles in series, AGMS, Deep cycle flooded and Starter type batteries all in one big pile....

Will this damage the TC battery types over time, or just affect the efficiency
of the charging from the truck alternator...

Forum Discussion

Combining battery sizes in parallel.

About Travel Trailer Group

Related Content

Parallel battery

Add third 12V battery in parallel to travel trailer?

All GM trucks combined sell more than Ford.

Legal to tow this combination in Alaska

Travel trailer GVWR more that combine GAWR