Can you have two battery banks on one solar controller?

[AndNeitherDoI]

Hey gang, I brought AGM batteries for my new 21C, and Escape left the dual flooded plate batteries in there. So now I have four 6v batteries - 2 AGM 6v 225 ah and the two from Escape. From what I can tell, putting all four batteries (two AGM, two flooded) in Series/Parallel is a bad idea.

Is there a way to keep both battery sets and use the onboard solar controller? I'd love to have the extra amp hours but don't want to create a huge hassle for these really heavy batteries. I'm betting I'll be better off just trying to sell these flooded plate batteries but I thought I'd check with the smart people here.

Thanks in advance!

[alanmalk]

Originally Posted by AndNeitherDoI

Hey gang, I brought AGM batteries for my new 21C, and Escape left the dual flooded plate batteries in there. So now I have four 6v batteries - 2 AGM 6v 225 ah and the two from Escape. From what I can tell, putting all four batteries (two AGM, two flooded) in Series/Parallel is a bad idea.

Is there a way to keep both battery sets and use the onboard solar controller? I'd love to have the extra amp hours but don't want to create a huge hassle for these really heavy batteries. I'm betting I'll be better off just trying to sell these flooded plate batteries but I thought I'd check with the smart people here.

Thanks in advance!

You are correct in noting that AGM batteries should not be in the same circuit at the same time as flooded batteries. One chemistry will likely try to charge or discharge the other, resulting in a dead battery.

Use a "1-Both-2-Off" switch to separate the two batteries.
The attached photo shows one example. Where it says "engine" you substitute solar charger. Solar will be charging the currently active battery - either the flooded or the AGM in this case. Avoid "both" for the reason mentioned above.

There is one fundamental problem: The solar charger has settings for flooded vs AGM and you may grow tired of switching it around to match your current battery selection.

You can get more complicated with isolators and other devices. Search on "battery charging isolator" to see some of the many options. Personally, I would keep it as simple as possible.
--
Alan

[Ron in BC]

I'm a great fan of redundancy and have two 12s forming two battery banks separated by a marine multi-position battery switch. I've had batteries fail and this way I always have a charged battery in reserve. I can select 1, both or 2. When I had a microwave in my 19 I would select both but with your batteries that's probably not necessary.

While the charge controller may have to be set to one type or the other it's not something you would have to do frequently. If redundancy is the name of the game then you would do the same as what I do. Use one bank for 2-3 weeks and at some point switch to the other bank so that it gets topped up.

Ron

[steve dunham]

Originally Posted by Ron in BC

I'm a great fan of redundancy and have two 12s forming two battery banks separated by a marine multi-position battery switch. I've had batteries fail and this way I always have a charged battery in reserve. I can select 1, both or 2. When I had a microwave in my 19 I would select both but with your batteries that's probably not necessary.

While the charge controller may have to be set to one type or the other it's not something you would have to do frequently. If redundancy is the name of the game then you would do the same as what I do. Use one bank for 2-3 weeks and at some point switch to the other bank so that it gets topped up.

Ron

Your method make the most sense in my estimation and eliminates the chance of all four batteries being connected at the same time — Safe , inexpensive and effective IMHO

[John in Santa Cruz]

the problem IMHO with that setup is the disconnected battery bank isn't being charged.

[LRL]

Originally Posted by steve dunham

Your method make the most sense in my estimation and eliminates the chance of all four batteries being connected at the same time — Safe , inexpensive and effective IMHO

This all appears to be a solution in search of a problem. I've not seen many posts on the forum over the past 4 years of batteries spontaneously failing, resulting in great relief among those who keep two sets sitting around just in case. Is it really worth the extra weight and extra hassle to solve a "lightning striking twice" sort of problem? If it is to you then by all means go for it. But I think you'll get more bang for your buck selling the flooded batteries and not giving them another thought.

[Ron in BC]

Originally Posted by steve dunham

Your method make the most sense in my estimation and eliminates the chance of all four batteries being connected at the same time — Safe , inexpensive and effective IMHO

The only negative that I can see is the weight of a double set of 6Vs. In my case there's not much of difference in weight between two 6s or the two 12s, not enough to be a consideration. If I lose one 12V I've still got a working electrical system. Lose one 6V and you've got a handful of nothing.

Originally Posted by John in Santa Cruz

the problem IMHO with that setup is the disconnected battery bank isn't being charged.

I haven't noticed any problem going even 4 weeks between switching banks.

Ron

[alanmalk]

Originally Posted by John in Santa Cruz

the problem IMHO with that setup is the disconnected battery bank isn't being charged.

Sigh. You could charge both banks with an isolator - but you just added more expense, more complexity, plus an obligation to learn about potential voltage drop if the isolator is a diode type, etc.

Yes, I did all that when living on a sailboat in "the old days". But having a powerful, working battery could have been the difference between getting my diesel engine started vs ending up on the rocks, or using my SSB radio to call for help. These days it is not necessary to lug 200 pounds of battery around just to boondock. A couple of solar panels provides ample power for most everything except air conditioning. Unless you're living in a cave you are going to have some sun for some part of the day. Personally I would rather lug around 200 pounds of bacon.
--
Alan

[Effie]

Originally Posted by LRL

This all appears to be a solution in search of a problem. I've not seen many posts on the forum over the past 4 years of batteries spontaneously failing, resulting in great relief among those who keep two sets sitting around just in case. Is it really worth the extra weight and extra hassle to solve a "lightning striking twice" sort of problem? If it is to you then by all means go for it. But I think you'll get more bang for your buck selling the flooded batteries and not giving them another thought.

Just what I was thinking.

[AndNeitherDoI]

Originally Posted by Ron in BC

I'm a great fan of redundancy and have two 12s forming two battery banks separated by a marine multi-position battery switch. I've had batteries fail and this way I always have a charged battery in reserve. I can select 1, both or 2. When I had a microwave in my 19 I would select both but with your batteries that's probably not necessary.

While the charge controller may have to be set to one type or the other it's not something you would have to do frequently. If redundancy is the name of the game then you would do the same as what I do. Use one bank for 2-3 weeks and at some point switch to the other bank so that it gets topped up.

Ron

That was excellent, thank you Ron!
If I do not find a taker for my batteries, I will probably end up doing this. Thank you.

[AndNeitherDoI]

Originally Posted by alanmalk

You are correct in noting that AGM batteries should not be in the same circuit at the same time as flooded batteries. One chemistry will likely try to charge or discharge the other, resulting in a dead battery.

Use a "1-Both-2-Off" switch to separate the two batteries.
The attached photo shows one example. Where it says "engine" you substitute solar charger. Solar will be charging the currently active battery - either the flooded or the AGM in this case. Avoid "both" for the reason mentioned above.

There is one fundamental problem: The solar charger has settings for flooded vs AGM and you may grow tired of switching it around to match your current battery selection.

You can get more complicated with isolators and other devices. Search on "battery charging isolator" to see some of the many options. Personally, I would keep it as simple as possible.
--
Alan

Thank you, this is very helpful! I think the isolator is going to be a bit above my comfort level but good to know there's more out there to investigate.

[sunrisetrucker]

Originally Posted by John in Santa Cruz

the problem IMHO with that setup is the disconnected battery bank isn't being charged.

I've been using two 12volt batteries for some time now and that's not even an issue. Arriving at my destination with 2 fully charged batteries gives me a good deal of satisfaction. Especially here on the wet coast where solar power can not always be counted on.

[Vermilye]

Since both battery types have different charging requirements, you may find you need to reset the solar controller each time you switch between them.

[rbryan4]

Sell the flooded ones. If you want redundancy, you could always add a 2nd bank of AGMs later on the 2nd circuit of the charge controller. Just my 2 cents.

[Ron in BC]

Originally Posted by LRL

This all appears to be a solution in search of a problem. I've not seen many posts on the forum over the past 4 years of batteries spontaneously failing, resulting in great relief among those who keep two sets sitting around just in case. Is it really worth the extra weight and extra hassle to solve a "lightning striking twice" sort of problem? If it is to you then by all means go for it. But I think you'll get more bang for your buck selling the flooded batteries and not giving them another thought.

I would agree that the having two banks of 6V batteries is a bit of an unusual situation but for the right circumstances it could be quite feasible but it's definitely not for everyone.

I disagree about the comment about batteries spontaneously failing. On my 19 I lost a cell in a battery that was less than a year old. Lose a cell, you've lost the battery. Fortunately I'd already installed my second 12V battery by then so it was only a minor inconvenience. Lose a cell in one 6V battery and you've got nothing.

Ron

[steve dunham]

I am of the same mind as Ron — When our dual 6 volt batteries reach the end of their useful life, my plan is to replace them with dual 12 volt AGM batteries
Our previous trailers had single 12V wet cell batteries and on two occasions we had cells fail leaving us dead in the water . The chance of both 12V AGM batteries failing at the same time is slim .
At this point in time and based on our usage, I cannot justify the cost of purchasing lithium ion batteries

[Perry Butler]

After almost 3 months, yes months, one of our 6v AGM's failed, all but ruining the other AGM. While we were trying to figure out the problem wintering in Arizona, I went to Costco and purchased a series 27 battery, that would be needed about 3 am. I alternated between batteries manually, until Crown agreed it was a failed 6v battery. When I took the batteries in for exchange they said the other battery was not in good shape (imagine that after numerous nights going down to below 11 volts). After 1 1/2 years our Crowns are still going strong. We now have a Victron 712 battery monitor, so this will never happen again (Murphy is now scared!).

Enjoy,

Perry

[AndNeitherDoI]

Originally Posted by rbryan4

Sell the flooded ones. If you want redundancy, you could always add a 2nd bank of AGMs later on the 2nd circuit of the charge controller. Just my 2 cents.

Mercifully, someone bought them today!

[rbryan4]

Originally Posted by AndNeitherDoI

Mercifully, someone bought them today!

[emoji106][emoji106]

[MBA80]

Zamp Solar makes a 30-amp dual battery bank controller. Also consider hooking the 6-volt batteries in series for more amp hours of power.