Custom Dual Battery Setup (AGM & Lithium) in a 4-Door Jeep JK

[theksmith 3,827]

i'm finally doing a dual battery setup in Gadget! it's going to be a slow project as i acquire a few pieces at a time.

 

 

motivation

 

i've managed to get by with just the factory battery and have a 12v fridge without too much trouble so far, so why the upgrade?

 

• be able to run the fridge for longer and colder without worrying. right now if i'm wheeling all day and only camped in the evenings, i can get by. but if i'm staying somewhere for a day or 2, then i need to let the rig idle multiple times a day to keep the OEM battery charged enough. i also constantly worry about it, so i'm always trying to be fast when opening the fridge and i run it a little warmer than i would really like.
• to run more power hungry stuff! i want to be able to use my 12v lunchbox style oven without the Jeep running. i also have a 12v blanket to put inside the sleeping bag when it's super cold out, and i want to get a cell phone signal booster (and maybe even a Starlink dish). all of these use a lot of current constantly - meaning they could kill a stock battery quickly if the rig's not running.
• eventually add solar panels to extend the setup for staying camped in one spot for even more than a day or 2.

 

 

 

the plan

 

i want to set this up very much like an RV, with the stock H6 AGM remaining as the "starting" battery, and a second battery acting as the "house" bank to power nearly all my aftermarket accessories.

 

key ingredients:

 

• i decided to go with a lithium "house" battery. the power density (usable amp-hours for a given size battery) of the LiFePO4 chemistry really seems worth the extra cost and system complexity.
• a dual battery isolator keeps one battery from discharging the other when parked, yet allows them to both charge when the engine is running.
• having 2 different types of batteries means i need a DC-DC charger. they increase the variable alternator voltage to the consistent higher voltage necessary to properly charge a lithium or gel battery.
• custom mounting solutions (bracketry) for all this new stuff.
• misc supplies including large gauge wire, fuse blocks, ground bus, etc.
  
  

 

additional nice-to-haves:

 

• a dedicated 120v AC lithium charger, so i can charge the house battery by plugging into "shore power" at home or in a campground.
• a battery monitor based on a current shunt to provide an accurate reading of how much capacity i have left in the house battery at any given time (or how much time is left till a full charge).
• when i'm ready to add solar, i'll need panels as well as an MPPT charge controller.

 

you might notice i did not mention an inverter. all of my major accessories are 12v, so i'm not currently planning to add a high-wattage AC inverter. the Jeep already has a small one built-in that i can use for low wattage things like a camera battery charger, etc.

 

 

alternatives

 

there's the traditional dual AGM battery in the stock location setup. you just need a dual battery tray from Rugged Ridge, MORE, or Genesis, along with some sort of isolator (simple solenoid, VSR or similar). those are great for a little peace of mind when running a fridge, but don't give you a ton of usable amp-hours for much else.

 

most people would probably be better off with a "solar generator" (portable battery pack). it comes out cheaper in the end and is obviously much simpler to get an all-in-one device than piece together your own dedicated system. the portability is appealing as well, especially if you have more than one adventure vehicle.

 

IMO, the Eco-Flow Delta series are the best ones right now. one big advantage is how quickly they re-charge from a standard 120v AC outlet versus the Jackery, Goal-Zero, etc.

 

 

the main reason i didn't go this route was the size. i'd be looking at a full sized Delta 1300 instead of the Delta Mini to get the Amp-Hours i want, and that one is a pretty darn big chunk. i really don't know where i could put it that i wouldn't have to move it every time i want to use my sleep platform.

 

they also charge slowly with the vehicle adapter, so you pretty much need solar to keep them topped off. i could work around that by feeding directly into the solar input from the alternator, but then i'd still need to wire up an isolator, and at that point it's turning into a custom install anyway.

 

i think the setup i have planned will provide plenty of power for multiple accessories, be mostly out-of-site, and work seamlessly with the rig, shore power, or solar power. stay tuned!

Edited August 12, 2022 by theksmith

[Stacey and Scott 1,164]

17 minutes ago, theksmith said:

i'm finally doing a dual battery setup in Gadget! it's going to be a slow project as i acquire a few pieces at a time.

 

 

motivation

 

i've managed to get by with just the factory battery and have a 12v fridge without too much trouble so far, so why the upgrade?

 

• be able to run the fridge for longer and colder without worrying. right now if i'm wheeling all day and only camped in the evenings, i can get by. but if i'm staying somewhere for a whole day or 2, then i need to let the rig idle several times a day to keep the OEM battery charged enough. i also constantly worry about it, so i'm always trying to be fast when opening the fridge and i run it a little warmer than i would really like.
• run more power hungry stuff! i want to be able to run my 12v lunchbox style oven without the Jeep running. i also have a 12v blanket to put inside the sleeping bag when it's super-cold out, and i want to get a cell phone signal booster eventually. all of these use a lot of current constantly - meaning they could kill a stock battery pretty quick if the rig's not running.
• eventually add solar panels to extend the setup for staying camped in one spot for even more than a day or 2.

 

 

 

the plan

 

i want to set this up very much like an RV, with the stock H6 AGM remaining as the "starting" battery, and a second battery acting as the "house" bank to power nearly all my aftermarket accessories.

 

key ingredients:

 

• i decided to go with a lithium "house" battery. the power density (usable amp-hours for a given size battery) of the LiFePO4 chemistry really seems worth the extra cost and system complexity.
• a dual battery isolator keeps one battery from discharging the other when parked, yet allows them to both charge when the engine is running.
• having 2 different types of batteries means i need a DC-DC charger. they increase the variable alternator voltage to the consistent higher voltage necessary to properly charge a lithium or gel battery.
• custom mounting solutions (bracketry) for all this new stuff.
• misc supplies including large gauge wire, fuse blocks, ground bus, etc.
  
  

 

additional nice-to-haves:

 

• a dedicated 120v AC lithium charger, so i can charge the house battery by plugging into "shore power" at home or in a campground.
• a battery monitor based on a current shunt to provide an accurate reading of how much capacity i have left in the house battery at any given time (or how much time is left till a full charge).
• when i'm ready to add solar, i'll need panels as well as an MPPT charge controller.

 

you might notice i did not mention an inverter. all of my major accessories are 12v, so i'm not currently planning to add a high-wattage AC inverter. the Jeep already has a small one built-in that i can use for low wattage things like a camera battery charger, etc.

 

 

alternatives

 

i should mention that most people would probably be better off with a "solar generator" (portable battery pack). it comes out cheaper in the end and is obviously much simpler to get an all-in-one device than piece together your own system. of course the portability is appealing too if you have more than one adventure vehicle.

 

IMO, the Eco-Flow Delta series are the best ones right now. one big advantage is how quickly they re-charge from a standard 120v AC outlet versus the Jackery, Goal-Zero, etc.

 

 

the main reason i didn't go this route was the size. i'd need the full sized Delta 1300 instead of the Delta Mini to get the Amp-Hours i want, and that one is a pretty darn big chunk. i really don't know where i could put it that i wouldn't have to move it every time i want to use my sleep platform.

 

they also charge slowly with the vehicle adapter, so you pretty much need solar to keep them topped off. i could work around that by feeding directly into the solar input from the Jeep, but then i'd still need to wire up an isolator, and at that point it's turning into a custom install anyway.

 

i think (hope) the setup i have planned will be mostly out-of-site and work seamlessly with the rig, shore power, or solar power. stay tuned!

We went with Genesis dual setup to keep from eating up any cabin space. Ran a 2 gauge cable to a distribution block in the back for the fridge and any other power needs.

[4x4tographer 2,711]

I'll be watching this thread closely for sure! Dual battery is in my future for sure the next time my JL's AUX batt craps out.

[theksmith 3,827]

On 7/27/2022 at 9:37 AM, Stacey and Scott said:

We went with Genesis dual setup to keep from eating up any cabin space. Ran a 2 gauge cable to a distribution block in the back for the fridge and any other power needs.

 

On 7/27/2022 at 10:41 AM, 4x4tographer said:

I'll be watching this thread closely for sure! Dual battery is in my future for sure the next time my JL's AUX batt craps out.

 

the Genesis seems like a great traditional dual battery setup. a configuration like that with 2 OEM or similar batteries and an isolator can help run some additional accessories and of course provides a backup battery to self-jump-start if the main dies.

 

the only reason i'm going with the extra complexity of a lithium secondary battery is i'm mad power hungry - give me all the amp-hours!

 

 

 

power density & the tradeoffs

 

an OEM H6 / group 48 battery typically is rated at about 70 amp-hours. however with a lead acid (flooded, AGM, or gel) you never want use more than 80% of the rated capacity or you risk damaging the battery. so you only get about 56 usable amp-hours max for that extra 45 pound battery. in fact, you don't even want to use 80% too often or you'll shorten the life of the battery - 50% to 60% DoD (depth of discharge) is a better target, in which case you're only getting 35 usable amp-hours most of the time.

 

100AH LiFePO4 batteries can be found of similar size, but half the weight. the real advantage is that most are fine being run down repeatedly to 80% or 90% DoD. so you can get 80 to 90 usable amp-hours consistently, and can do that full cycle thousands of times instead of the few hundred that an AGM can.

 

the downsides to a lithium battery setup are higher initial cost, needing an additional DC-DC charger component to charge to their full capacity reliably, and they cannot be stored in the engine bay. 

 

why not in the engine bay? because a LiFePO4 will shut-down above 140*F. i don't mean just "it's bad for them" - their internal BMS (battery management system) will turn them off completely above that! note they have an even narrower temperature range to charge within, between 32*F and 113 to 130* depending on the brand. there are versions with a self-heating feature so you can charge in really cold weather. that's not a huge concern here in the southwest, but the complete shut-off at 140* is a real limiting factor, and thus my second battery will need to go in-cab.

Edited August 5, 2022 by theksmith

[theksmith 3,827]

 

the brain

 

i purchased a Renogy DCC50S to handle several tasks with a single device. The core feature is a 50A DC-DC charger to keep the lithium house battery topped off when the rig is running, and there's a smart disconnect (like a standalone VSR) to isolate the 2 batteries when the rig is off.

 

this also has an integrated MPPT based solar charge controller to handle charging the house battery from solar panels. a nice bonus feature is that once the house battery is full, it will switch and maintain the starting battery with a trickle charge from the solar input.

 

having an all-in-one device normally means some compromises versus getting separate best-of-breed components. however, the only spec i see on this that is a little weak is the max solar input voltage of 25v. that just means if i ever want to use multiple solar panels then i can only connect them in a parallel configuration (there are pros/cons to connecting them in serial or parallel). it should be fine for my needs, but i wouldn't recommend this for a larger van-life type build.

 

the Renogy can also connect to either a small LCD screen type monitor, or to a bluetooth module and then use a mobile app to monitor it. i'll likely go with the app method since i have a dedicated tablet already in the Jeep.

[Stacey and Scott 1,164]

I need to finish setting up a plug to connect the rig to the panels (make it quick and easy). I have found that one (have 5) 100 watt panel will get my secondary battery back to a full charge in about 4 hrs of good sun after a full night of fridge and lights. Still thinking about a 300 amp alternator, just in case 🤔

[jgaz 545]

17 hours ago, theksmith said:

 

the brain

 

i purchased a Renogy DCC50S to handle several tasks with a single device. The core feature is a 50A DC-DC charger to keep the lithium house battery topped off when the rig is running, and there's a smart disconnect (like a standalone VSR) to isolate the 2 batteries when the rig is off.

 

this also has an integrated MPPT based solar charge controller to handle charging the house battery from solar panels. a nice bonus feature is that once the house battery is full, it will switch and maintain the starting battery with a trickle charge from the solar input.

 

having an all-in-one device normally means some compromises versus getting separate best-of-breed components. however, the only spec i see on this that is a little weak is the max solar input voltage of 25v. that just means if i ever want to use multiple solar panels then i can only connect them in a parallel configuration (there are pros/cons to connecting them in serial or parallel). it should be fine for my needs, but i wouldn't recommend this for a larger van-life type build.

 

the Renogy can also connect to either a small LCD screen type monitor, or to a bluetooth module and then use a mobile app to monitor it. i'll likely go with the app method since i have a dedicated tablet already in the Jeep.

Kris,

Thanks for  including the link to the  “pros/cons” article.

I was trying to explain this very subject to a non tech friend that is setting up his RV to do longer off grid trips.

The article does a way better job than I was doing.  I’m no teacher

[theksmith 3,827]

the heart (lithium battery)

 

there's a ton of choices in the lithium battery market, within a huge range of prices - a 100AH LiFePO4 can be had anywhere from $300 to $1000!

 

other than personal experience from a trusted source, length of warranty seems to be the main way to judge quality on the many brands. however note that most manufactures also stipulate a number of cycles (2,000 to 4,000 typically) within the warranty details. be sure to consider whether some random company is likely to even still be around for a warranty claim in 5 or 10 years as well. besides cycles and warranty, the maximum charge/discharge current rating can also be an indicator of the overall quality.

 

batteries with built-in bluetooth are becoming more common, as well as with self-heating capability (for charging in cold weather). bluetooth is actually a pretty cool feature to help keep track of overall battery health with an app. it can also give you an idea of capacity at any given time without needing a separate battery monitoring setup.

 

anyone shopping for a lithium battery should check out the "DIY Solar Power with Will Prowse" channel on youtube - tons of great info and teardowns on various brands.

 

 

brands / cost

 

it's seems well accepted that SOK Battery is the best bang-for-buck LiFePO4 battery right now, and they're right in the middle of the pack on price. their standard 100AH goes for $570 or one with bluetooth and self-heating is $600. note that they've got a somewhat unique shape/size and terminal location.

 

Battle Born, and Dakota Lithium are a couple higher-end brands that i've heard good things about, with a 100AH coming in around $900 for either company. most of the random chinese brands on Amazon are around $450. battery technology is moving fast right now and so the prices keep falling further every few months.

 

 

size & shape

 

most of the 12v 100AH i looked at have just under a 13" x 7" footprint and are around 8.5" tall. i found a few with a smaller footprint of around 10.25" x 6.7". for example Power Queen sells both sizes on Amazon, with the smaller one listed as their "premium" version. there's a detailed review form one person on the smaller one and he was able to get the full rated capacity out of it. i can only guess that advances in manufacturing are making smaller cells possible now.

 

 

while looking at options with the smaller footprint, i ran across Dobelay who was selling their small footprint 100AH at $600 on Amazon but with a 50% coupon at the time. other than a few good reviews, they are a total unknown quantity and don't even have a decent website. but for $300 and the right size/shape to fit where i want to put it, i decided to gamble - if i even get a few years out of it then it will have been a good deal. i'll update this thread if it turns out to be a total POS or not deliver the claimed capacity.

[theksmith 3,827]

where to stick it

 

i think i've found a good place to put all this stuff. there's a decent chunk of unused space above the driver side rear wheel well (behind the back seat, between the fridge and outside wall, under the Front Runner cargo platform).

 

  

 

i'm planning to build a shelf style mount there and hope to fit the lithium house battery, Renogy DC-DC charger, fuse panel, battery disconnect, battery monitor shunt, and a 120v lithium charger. the shelf will be a similar design to this Morryde ammo can mount:

 

 

i drew up the pieces for this and will have them laser cut out of aluminum sheet by SendCutSend. they could also do bends, but to save money i've designed it in more pieces with all the areas that need bending to be less than 6" long tabs so i can do them myself using my vise brake. 

 

 

everything will bolt together with 1/4"-20 rivet nuts and socket button head bolts. i'm currently just waiting to get the lithium battery in hand and verify its measurements before i order all these pieces.

Edited August 2, 2022 by theksmith

[jgaz 545]

What gage aluminum do you intend to use on your parts?

 

If you want to design the pieces without the 6” restraint you  are more than welcome to try my Harbor Freight brake I detailed here.

It will handle 16 gage aluminum in lengths of a foot or more.

Even if you leave the <6” tabs it might be nice to bend both tabs at the same time.