JimWPB

A few days ago, I used a high volume 12vdc compressor to fill up my tires after airing them down to get bigger contact patches for over sand use. My battery got dragged down pretty far. The compressor draws like 75 amps & it takes like 8 or 10 minutes to fill all 4 tires. That got me wanting to either up-size my battery substantially or go to a duel battery system.

In the past, I have installed a massive D8 battery in my 1-ton pick ups, or installed a second group 27 battery with second alternator in my CJ-7's. When I look under the hood of my JK, I see a little group 48 battery that has a silly little 70AH rating. That explains where the issue originates. In my world, that's a small battery. What I didn't see was a lot of extra room to add more stuff. I MIGHT be able to squeeze in a group 27 where the 48 now sits & get my AH rating up around 100, but that's about it.

Looking around, I found an aftermarket kit that put 2 batteries in a custom tray with just a little cutting of factory original equipment & also added a management system that controlled isolation & charging. That was around $600-700 for the hardware, not including batteries. That seemed like an option except that the batteries were both smaller than the original & they wanted you to use 2 of the exact same battery. I really want to have one start rated battery & one deep cycle rated battery.

I am able to fabricate a system like this myself if I have to, but I'd rather buy something off the shelf if I can. I'm wondering what's out there & what other people have had good luck with. Right now, I'm leaning towards adding a Lithium battery inside the cabin & charging it with an echo charger that is programmed to only kick on when the main start battery sees charging voltages in excess of 13.7vdc. I'd really like to find other options though. I'd really like to find a plug & play solution.

resharp001

I just installed a dual battery setup in my jeep a few weeks ago. My primary purpose was being tired of fridge running on my starter battery. I also run an Arb dual compressor, winch, and various other accessories. Anyhow, I ended up going with the Rugged Ridge tray in my '13. It will fit two factory size batteries side by side. You do have to chop up your factory battery box cuz you re-use the portion for the fuse box. It is a very tight fit, but I can tell you that I've removed the passenger side VC enough to know that the battery tray needs to just come out regardless, and this is setup isn't going to be any harder than removing the factory battery tray. Also, the price the RR tray was made it not worth my time to fabricate something myself.

this is what I ended up with as a result -








I did not like that this tray uses a strap to hold the batteries in. i fabbed up a quick braket to hold the the batteries down and provided me a place to mount my 80-amp fuse blocks and isolator. the evap purge valve got relocated to a tab the tray provides for it, and I relocated the big electrical harness that sits on the factory tray up to the firewall.


****i will also add that for years I ran my Arb compressor off my starter battery....probably since 2015, maybe 2016. Anyhow, I always just left the engine running while using that and never had any issues filling up 37s from below 10psi.

JimWPB

Thank you. That's the best option I have seen so far.

I'm using a "Thor's Lightening" which is probably similar to your ARB double pump. My other existing heavy load of concern is a winch. ...but a 12vdc refrigerator may come along for the ride some day as well.

Nice install. That's a clean looking set up & you left yourself lots of room for future additions with no hassle. I like it.

resharp001

it's certainly tight. there is not much room between the isolator and the hood, but there aren't a ton of great options in the engine bay. the most space is over on the driver's side firewall but I didn't want it that far away.....so I ran into the opposite issue. being that close to the terminals creates a situation where you have to bend those thick wires pretty tight to get there where you want them. then, those 80-amp fuse blocks are pretty big. the biggest obstacle I had is that the battery terminals are recessed and raising them up to use the nice multi-port blocks just adds more pieces to the puzzle.

I just got back from a long trip up to Durango and Ouray. I can say the fridge doesn't last a whole lot longer on the AGM battery due to the fridge's low-voltage cut off. I get about 36-38 hrs of not moving I think before it starts cutting off, BUT, it is really nice to not have it on the starter battery. about 20-30 minutes of driving seems to get the auxiliary battery full charged again. I'm not doing full blown overlanding and my jeep is never sitting idle for more than a day with the fridge while on a trip, so for me this is adequate for now. Not thrilled about adding more weight though. I had considered going the LiFePO4 route, but seems to have it's own obstacles.

I have a Dometic CFX3 45 fridge. Moving from a cooler to a fridge was life-changing. it was an expensive jump, even getting at cost through buddy, but no regrets at all.

JimWPB

I've used LiFePO4 in some marine applications. They are a good fit for a 12vdc fridge. They operate at a slightly higher voltage than lead acid & the voltage curve is more flat. The energy density is about twice what you get with lead & the weight is not far from half as much. You can get a 100 amp hour "mini" that is about half the size of a group 31 & has the battery management system (BMS) built in. The price is now below $3 per amp hour, which is a big change from a couple of years ago.

There are some things to be careful of. They have a very high acceptance rate & can fry some charging systems. They like different charging curves & different finishing voltages compared to lead. Bad things happen whey you charge them when they are too cold or too hot. They degrade internally when they sit fully charged or fully discharged for long periods of time. Bad things happen when you over charge them. They are happiest when they run in the range of 20-80% state of charge, but 10-90% does not beat on them nearly as badly as a 40% charge would beat on lead, via internal sulfation.

Lithium needs a BMS to prevent the battery from experiencing events that would cause bad things to happen. bad things = fire & other serious issues of this level. BMS systems are not all alike. Some have low temperature cut off. Others do not. Different systems cut off at different draw or charge currents. The batteries in the standard BCI case sizes with the BMS built in are called "drop in batteries", but it's not always as simple as just changing the battery & calling it a day. When a BMS drops out to protect the battery from bad things happening, it just opens a contact & the battery looses contact with the outside world. This will fry the voltage regulators or rectifier diodes on many types of alternators. ...and the voltage regulator on your stock alternator probably doesn't put out the charging curve that a LiFePO4 will want anyway. Really good BMS systems will give you a few seconds warning before dropping out so that you can kill the field in the alternator before damage is done, but those BMS systems are few, far between. and generally not cheap.

A BMS on a 100AH lithium battery will likely kick out on over current somewhere between 50-100 amps. They are not good start batteries, unless you put in a really big bank of them. If you bank up 800AH of LiFePO4, then you can start a motor. ...and you can run your fridge for more than a week straight with no charging.

Lead likes to be brought up to 100% state of charge on a regular basis. That includes valve regulated batteries, also known as AGM & Gel cells. They don't like to operate below 50% state of charge. Ignoring these realities results in sulfation and internal shorting. Slight cases of this can be reversed to a certain extent with special charging techniques or "repair functions" on some chargers. Once the sulfur bridges the bottoms of the battery plates, it's kind of to late. If you see a bulge or feel the battery getting warm while just sitting there powering nothing, it is way too late & starting to get dangerous. In extreme cases I've seen ruptures & I've seen smoke coming out of a lead acid battery. Since lead doesn't like to be run down past 50%, the ratings on lead batteries are actually kind of bogus. In a 100 amp hour lead battery, you really only get to use 50AH without measurably damaging the battery.

AGM has a higher acceptance rate than flooded lead acid batteries, but they have a slower finishing charge curve & they suffer more than FLA if they are not brought up to full charge daily. The flooded batteries actually take a beating electrically a little better than an AGM, but the AGM takes a physical beating better, almost can't leak acid & gets back up to 80% state of charge much faster than flooded, but not nearly as fast as lithium. Lithium doesn't care if it never sees 100% soc. Unlike lead, it's happiest at or near 50% all day every day. I say that AGM ALMOST can't leak because they actually have a safety pressure relief valve built in & if that blows, then the acid inside goes for a ride into the outside world. It's pretty rare. It can happen if you abuse them badly enough.

Dometic makes good stuff. I've used several of their products. The guys that come close on quality for a little less are Engel & Iceco. There is also a lot of low-end off-shore stuff out there that is not in the same class.

Sandau

resharp001

@Sandau is always good with electrical commentary. looks like using the RR tray as well, based on the post that evap purge is on. Clean install. I just couldn't justify the cost of 2 yellow tops for my use.

Sandau

I couldn’t justify it either😮‍💨😆

wonderd

I just ordered myself lifepo4 100A cells and 60A bms. Also bought a vsr to disconnect the lfepo4 from main battery when engine is off, so the main doesn't drain.
the idea is to have a battery installed in the back of the jeep, connected to fridge, water pump, camp lights and compressor if needed without disturbing the main one.

resharp001

I really debated about the LiFePO4 route myself. At the end of the day I wasn't willing to have a battery taking up space in the back anywhere. Most of the longer trips I trips I take in the jeep have 3 people in there, and all the stuff for 3 people on top of fridge and all the supplies. It can get pretty tight even with one of the rear seats folded down. When I really thought through things, I wasn't getting a whole lot longer run time on LiFePO4, AND it was taking up interior space. I do think those are interesting batteries though. We are certainly getting to a point in battery technology where there are other options for these setups, and that is really nice.

Please share your install and experience if you head down that path!