Pop up camper, expanding existing deep cycle battery with additional AGM batteries?

[ADDvanced]

Alright, here's the sitch:

I have a camper with a bigass deep cycle 12v battery, lead acid.

My skoolie (entirely different system) has two AGM batteries like this, but I'm replacing those with lithium, which means I will have two of these laying around, to be USED ON THE CAMPER???

https://amzn.to/44OGV9g

Now the camper has a built in ... charge controller... thing. Basically if you plug it into shore power, it will charge the battery mounted on the tongue of the camper, and when you unplug the shore power, the lighting and fan and furnace and stuff will run off that battery.

I'm wondering how I could combine these two battery types, I have room in the camper for sure.... but right now the camper does NOT have any solar or anything.

Just wondering if anyone has successfully tacked on another bank of batteries to an existing pop up like this before. I realize I could get a battery isolator, but I think the charging profiles of just a lead acid vs an AGM would be different, no?

 

[yodamota]

flooded lead acid and absorb glass mat do have different charging profiles.

 

[MisterSandals]

I'm wondering how I could combine these two battery types

There are a number of ways to make the useful without actually combing them.
What will your lithium bank be? Will it be charged with solar routinely?
Will you be plugged into shore power often or will they normally need charging (like from your lithium bank)?

Just trying to learn about your system before making a recommendation.

 

[Tomthumb62]

One idea is if your 12v loads are low, with just things like LED lights, water pump, kitchen exhaust fan and not high draw like hydraulic levelers, then you could use your AGMs to power that, separate from the lithium. Use the lithium to power the inverter AC loads. Not sure how your shore power converter thing would fit into that scenario, because I don’t know if it separates AC and DC loads for two different battery systems as I think they’re usually designed for single battery bank systems. I’m sure a resident RV expert will chime in soon. MisterSandals is a pretty smart person.

 

[ADDvanced]

There are a number of ways to make the useful without actually combing them.
What will your lithium bank be? Will it be charged with solar routinely?
Will you be plugged into shore power often or will they normally need charging (like from your lithium bank)?

Just trying to learn about your system before making a recommendation.

No lithium. I have a skoolie that currently has the two AGM batteries, but it will be upgraded to lithium shortly.

Then I will have the two AGMs sitting around doing nothing..... and I have this camper iwth one deep cycle, don't have the specs. Just trying to figure out how to utilize the AGMs instead of selling them.

 

[ADDvanced]

One idea is if your 12v loads are low, with just things like LED lights, water pump, kitchen exhaust fan and not high draw like hydraulic levelers, then you could use your AGMs to power that, separate from the lithium. Use the lithium to power the inverter AC loads. Not sure how your shore power converter thing would fit into that scenario, because I don’t know if it separates AC and DC loads for two different battery systems as I think they’re usually designed for single battery bank systems. I’m sure a resident RV expert will chime in soon. MisterSandals is a pretty smart person.

No lithium here. Please forget I said anything about upgrading an entirely different vehicle/system to lithium.

 

[Craig]

do you know how many amps the onboard charge controller uses. I would get an inverter that runs off the AGM batteries and plug the onboard charge controller into that full time. Then get another charge controller that will charge your AGM's from the trailers shore power. this may waste energy though IDK. but it would keep the different chemestries isolated. all this assumes that the onboard charge controler is not programable. If it were I would just run them all in parallel and find a profile that kind of works for both chemestries. But then again I just do what I want I dont like to follow rules.

 

[ADDvanced]

That's an interesting idea. It is wasteful, but it would make a robust system. I'm just not sure how much capacity it would add after running DC to AC back to DC.

Right now I have access to a 230 watt solar panel, and a 100 watt panel. I'm not sure how i'm utilizing those yet; I am likely going to permanently mount one on the exterior of an open A-frame that will help shield the trailer from snow loads.

 

[Craig]

well if you have solar available I would definitely charge the agm from that . I dont think its gonna waste all that much energy but obviously wouldnt be ideal you could add a switch to turn off the inverter when not charging to save some power. But it would be down and dirty easy and quick. How many amps does the onboard charger draw IMO the inverter size/cost would be the deciding factor.

 

[ADDvanced]

What about a DC to DC charger? Would that be more efficient?

 

[MisterSandals]

What about a DC to DC charger? Would that be more efficient?

I was thinking this could be a good solution if one battery is more likely to be charged (by solar or shore power) but you have not revealed much about your situation.

 

[Craig]

Not sure DC to DC would work as the voltage differential wouldn't be enough and it may cause some sort of loop.

Existing batteries -> DC DC ->AGM-> Existing?

 

[SamDeleted]

skoolie

Is that millennial for school bus ?

 

[STW]

You can charge lead acid with AGM profile without harm. Charging AGM with lead acid profile might harm the AGM… I say might because these profiles are close. You want to prevent gassing in an AGM, so it takes a little less on the voltage side. You would definitely lower the charge amps per battery when you parallel the AGMs in the mix since there are more batteries getting charged, so check what your charger puts out to make sure it charges as fast as you want.

I wouldn’t be too worried about connecting them together. My motorhome has 4 AGMs for house and 1 lead acid for starting. They all get charged by the same charger at the same time.

 

[STW]

That's an interesting idea. It is wasteful, but it would make a robust system. I'm just not sure how much capacity it would add after running DC to AC back to DC.

Right now I have access to a 230 watt solar panel, and a 100 watt panel. I'm not sure how i'm utilizing those yet; I am likely going to permanently mount one on the exterior of an open A-frame that will help shield the trailer from snow loads.

Mixing panels to a single controller normally doesn’t work well. It would be better to have 2 separate controllers. Both controllers could be connected to same battery bank. Expect to get about 15 amps total from the two panels.

 

[mikefitz]

Put them in parallel with your existing battery , the charging and float voltages won't cause any issues.
If your AGM batteries are more than 2 years old they may have lost significantly capacity and perhaps not worth the effort of installing.
Capacity testing all your lead acid batteries would be a useful exercise, the actual capacity may be much less than you expect.

 

[ADDvanced]

I was thinking this could be a good solution if one battery is more likely to be charged (by solar or shore power) but you have not revealed much about your situation.

I don't have a situation yet. Just trying to figure out what makes sense to keep everything topped off when I'm not there for months at a time, and keeps the batteries topped off when I am there using it.

 

[ADDvanced]

Put them in parallel with your existing battery , the charging and float voltages won't cause any issues.
If your AGM batteries are more than 2 years old they may have lost significantly capacity and perhaps not worth the effort of installing.
Capacity testing all your lead acid batteries would be a useful exercise, the actual capacity may be much less than you expect.

How do you do capacity testing without flattening them? Have a link? I'll google it now.

 

[wme]

Does you popup NEED more power? What is the AH rating of the lead acid vs the pair of AGM.
K.I.S.S.

 

[Rednecktek]

Does you popup NEED more power?

Well DDUUHH!! How else is he gonna run the MargaritaMaster-9000 while boondocking?!?!

I'm still a fan of just building a nice 280 or 304Ah LFP battery and mounting that out front.