I've thought about this way too long and I cannot make a decision on whether to get a cheap lifepo4 or lead acid 12v for my otherwise 24v system

[joshjhayes]

Budget is a big consideration because I would much rather be putting money into expanding my 24 volt battery bank. I currently have 100ah of 24 volt. I have a 15 amp solar charge controller charging my current SLA with the 24 volt system as the source. It's an RV so I need the 12 volt to run the lights, slide out, Happy Jack bunk, furnace etc. Theoretically I only really need the battery if I ever go beyond the 15 amp of the charge controller. I'm leaning towards SLA because I could still charge with alternator with no modifications. Budget is $100 or less. Concern with going lifepo4 is cold weather at that low price wouldn't have charging cut off. I'm thinking that SLA would last really long because it would spend almost all of its time at full charge. I know it's really stupid that I spent so much time thinking about this question. Your help is appreciated lol.

 

[Samsonite801]

I might recommend to go find a local battery reconditioner, or another option like FB Marketplace or Craig's list to just buy some used SLA in decent condition, to get by for long enough to save and build a LiFePO4 based system with heaters and cold weather protection later. In the long run, LFP saves more money, they last longer (more years and cycles), they can go much deeper DoD, and less round trip efficiency loss...

 

[timselectric]

Maybe a 24v to 12v converter? And lose the extra battery all together.

 

[hwy17]

You already have this setup with a lead battery in that spot and it works for you? I'd stick with it then.

 

[cinergi]

I agree, stick with what's working. In my RV my primary battery is 48 so I need 12v, too. I would have built it with a 48/12 converter but the jacks and slides require 100-150 amps alone and would have been difficult to source a good converter capable of that kind of amperage... PLUS, you're supposed to have a 12v battery source for the emergency trailer brakes and while I'm not sure a 48/12 converter qualifies for that, it's another big 12vdc load when activated... so I used a 12v LFP battery that a 48/12 30 amp controller keeps topped off. It's on the edge of my highest loads though -- the 12v battery max is 100 amps plus the 30 from the converter means I technically max out at 130 amps (until I exhaust the battery but I don't draw >30 amps for long periods of time).
I don't worry about the truck charging the 12v battery. The 12v loads are too insignificant while driving for this to be of any value.