DIY LiFePO4 Battery for Jeepy

Working on a cool project for the KK.

I built a trunk box with a tool drawer back in 2014, and it has some additional space behind the rear seats for a washer fluid bottle and some picnic blankets. It started out as a drawing and ended up being made out of wood.

The trunk, measured very carefully:


Box design:


The real thing being built:


Carpeted to match the Jeep's interior. This is the forward view showing the cubby behind the rear seats.


And installed. The drawer stores tools, recovery gear, and a first aid kit, among other things.


In 2024 I am repurposing part of the space behind the rear seats by building a custom lithium iron phosphate battery that will live back there. It will power my camping fridge and charge using solar panels on the roof rack. It will also run an inverter. Basically it’s a DIY solar generator that fits in my KK. At 74 amp hours I can power stuff even when the Jeep is off. I promised to post some pics of the project so here you go.

This is the battery box I built.
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It fits 4 lithium iron phosphate cells, which together make a 12 volt (13.2 volt nominal) battery. This one stores 74 amp hours.


Test fitting it in the trunk box behind the back seats ... it fits! And there is still room for a bottle of washer fluid.


Next came actually building the battery. The cells have to be monitored and protected by a battery management system (BMS) computer so they don't under or over charge. I mounted the BMS on the front face of the box. It is on the right side. On the left is a 5 inch touch screen. On the top of the battery you can see how I tied the cells together using copper buss bars that I made. Under that red hooded thing is a 100 amp MBRP fuse for safety.


A closer look at the front. The touch screen displays a readout of the battery and its various components, as well as lets me change the battery settings. The computer that runs the touchscreen is a Raspberry Pi 3B+ which you can buy for $40. It's running Victron's Venus OS. The Raspberry Pi is attached to the left side of the box. In this photo it still has some blue painter's tape on it. Oops! So much for professional looking images.


The Raspberry Pi's power source is the black box on the lower left. It converts 12 volt to 5 volt power, which is what the RPi uses. The blue box directly under the RPi is a Victron smart relay. The relay turns on two beehive heating pads that are located under the battery cells, to keep them warm when charging the batteries in winter. It turns out LiFePO4 batteries cannot be charged below freezing without killing them. The RPi senses the battery temperature and controls the relay, which activates the heating pads when the batteries are below 39 degrees F (2 degrees C) and it wants to charge them.


On the other end of the battery is a fuse box with 6 circuits and ATO fuses. Right now the two fuses you see are for the battery heater and the Raspberry Pi computer. The 4 other circuits will be for front and rear 12 volt outlets, as well as rear flood lights and front ditch lights (which don't exist yet but hopefully will soon). The idea is to be able to keep devices and lights on for a long time without having to idle the Jeep's engine or kill the starter battery. The 12 volt outlets will be for my camping fridge, as well as charging phones and computers. I do a lot of camping for my field work and research as a forest ecologist, so these things will be helpful.


Here is the whole battery in front of a 20x40" solar panel (100 watts) for scale. The battery is actually pretty compact and small. I'm going to mount a couple of these 100 watt panels on the roof rack and run them in series. I like the idea of not having to run the Jeep to charge the battery. I know I could use a DC to DC converter to charge from the Jeep's alternator but I already had a solar charge controller and the two panels kicking around the basement. Plus it will look cool.


The solar charge controller is on the left and a 375 watt inverter is on the right. The inverter has a household GFCI outlet with a pure sine wave output, which is a very clean power source (no buzzing or distortion). The inverter could run power tools or my coffee grinder, or charge anything with a 120 volt power brick. Coffee is not optional when camping. Those devices will live on the side of the trunk box, where the Jeep's amplifier would be if it came with that option (it didn't).


Finally here is the battery in its new native habitat. It will be bolted in securely and will be completely invisible when the rear seats are up. The battery's touchscreen can be accessed by putting the passenger rear seat down or by using Victron's bluetooth connectivity on a smart phone.


The two solar panels will be installed up here. I am still working on how to route the solar power cables into the cabin without drilling.

I just finished the building battery itself tonight, and the installation in the Jeep will be coming up.

Nice and clean! Good stuff!

For your next trick … plug your house in and run your fridge in the next outage.

Noice!

Impressive, but living in the land where the sun doesn't always shine I'd have a split charge from the alternator too so when I arrive I have a full battery to start with, my caravan is setup like this.

that is one great setup!

Looks very clean and well designed. Can’t wait to see more on this.

Nice! What was your investment in all the parts vs a complete battery?

I think I am coming out pretty well on cost. Something like an Ecoflow or a Jackery can be pricey. For size comparison, my battery has about 1000 watt hours (a tad less; 74 amp hours x 13.2 volts nominal = 976.8 watt hours).

The four 74 Ah battery cells and the 100 Amp BMS came from Battery Hookup. The cells were about $32 each (x 4 = $128) and the BMS was $75.

The wood for the battery box and the pocket screws were already in my possession. The 1/8” x 1” copper strap for the buss bars was left over from another battery project for my camping trailer, and so were the lock nuts to hold the buss bars onto the cells. I was also using wiring terminals and battery cables I already had, although let’s say I had to buy $50 in battery cable lugs and wiring to be able to connect everything to the battery. The Waveshare 5 inch touchscreen was $52 on Amazon.

That brings the battery itself to $305. The solar charge controller was left over from another project and got it as a free item when I was buying solar panels on Craigslist. The 375 watt inverter was a new purchase from Inverters R Us and was about $145 if I remember correctly. The solar panels were siting in my basement from another project too, so they were free. Initially I paid $100 for them on Craigslist but it was a while ago. The Raspberry Pi computer was sitting on my shelf for 2 years collecting dust, so I put it to use. Victron’s Venus OS for the Raspberry Pi is free to download and use.

All together, I’m calculating a total of $450 for the components that would be inside a solar generator off the shelf, or $550 including the solar panels. In reality it would cost more if I didn’t have a bunch of stuff left over from other projects. But a 1024 watt hour Ecoflow Delta is $969 on Amazon now without solar panels, which are currently going for $175 for a pair of Renogy 100 watt panels. A similar wattage Jackery is $599 right now on Amazon but it is a special sale. The Ecoflow and Jackery would both contain a charge controller and an inverter as part of their package, but not solar panels.

Either way, I think I win in terms of cost and in the fun of designing it and building it. I think I began thinking about doing the project back in May so it has taken me a while to get here. I’ve mostly been working on it in the evenings after supper and after washing dishes, and before bed. I like that it’s a little stealth unit that fits inside my Jeep in the space I had behind the seats.

Today I had a few hours to work on the battery project and begin to install it in the Jeep.

Job one was to install a vehicle-spec fire extinguisher bracket, since there is an increased risk of fire with an extra electrical system. I made a base plate out of aluminum that bolts underneath the bracket, so it's not going anywhere without taking the whole plastic molding with it. Safety first. I was able to reach up there through the jack compartment to install the washers and nuts on the bolts.





Next, the electrical system. In the photos above I put the rear seats down and pushed the trunk box forward. This is how I would access the jack as well as the spare tire winch in the event of changing a flat. It also allowed me to install the inverter and solar charge controller on the side of the trunk box through the passenger's rear door. The components fit nicely in the slot where the subwoofer/amp would be in a fancier version of this Jeep.



With the trunk box pushed back into its rearward position, this is how the components sit:



The picture above was taken from the back seat area looking to the rear. The solar charge controller is closest to the camera and the inverter is in the background. The side of the inverter with the household 120 VAC outlet faces the rear hatch for easy access.

The cubby to the right of the solar charge controller is where I installed the battery unit. It is securely bolted in with 4, L-brackets and 8 bolts. The bolts screw into T-nuts that are on the back side of the wooden partition, so the battery can not move.



As of tonight the charge controller and inverter are not yet wired up to the battery. That will be the next step. After that I need to install solar panels on the roof rack and get them hooked up to the charge controller. After that I have 12 volt power outlets and USB chargers to install in the front and back of the Jeep that can run a camping fridge and charge phones for days (or hopefully indefinitely with solar). There is room for expansion in the fuse box and I hope to get rear flood lights and front cowl lights at some point that will be hooked to this system. I could run the lights at night to light up a campsite without worrying about running the Jeep's regular battery down and getting stranded.

One last pic will show how the battery unit sits when the back seats are in the upright position. The whole aux electrical system is stealth.

Looks great and the battery setup is amazing.

I made a box for mine and really enjoying the extra storage and function.

gvaldez said:

Looks great and the battery setup is amazing.

I made a box for mine and really enjoying the extra storage and function.

Click to expand...

Thanks! I got the inverter and solar controller wired to the battery today. Yay! They work!

Excited to be able to put this battery to use with my camping fridge. What do you use yours for?

Wow! This looks amazing!
Nice work and electrical skills

Did a little bit more on the battery project today.

I got the solar wiring up to the roof rack in preparation for putting two 100 watt solar panels up there. Right now I just have the 10 AWG wires zip tied in place and the two ends hooked together to keep the connectors waterproof. The wires are not connected at the other end to anything so there is no risk of a short circuit.



I ran the wires down the side of the tailgate and up past the weatherstripping at the bottom of the hatch. If any water is running down the wires during a rainstorm, it should drip off and not travel into the cabin.



The solar system is designed to be unhooked when pushing the toolbox forward. The two MC4 connectors you see in the background underneath the inverter go to the solar charge controller. The round thing in the foreground on the right is a GPS antenna. It is magnetic and is hanging out on one of the metal tie-downs.



I put MC4 splitters between the connections in the previous photo so that I have a way of hooking up an additional 200 watt suitcase solar panel if I want. That would double the wattage to 400 watts of solar, which is about 28 amps at 14.5 volts charging the battery.

Going to try and install the solar panels today and start charging the battery back up. I did a bunch of measuring and drilling on the solar panel frames for the tube mounts tonight and if I measured right, it shouldn’t take too long to bolt them on.

Finished getting everything together just as it got dark! But the solar panels do show some voltage from the street light, so they are alive!!!

I used some beefy tube clamps on the ATH roof rack, and tied them to the solar panels with some beefy stainless hardware.





Here's how the brackets look on the roof rack. I like how strong but also how low profile they are.





And here are the panels setting in place. I finished bolting them up after the sun went down. It was harder than I thought it would be to get under the panels with my wrench and ratchet, and also with the hex key to tighten the tube clamps around the bars.



The electrical connections are hooked up too and zip tied into place. The battery's at a very low state of charge so I will see tomorrow morning if it works as intended!

Excited to be able to have a camping fridge going 24/7 when I want to, plus charge phones, computers, gps units, etc. without worrying whether I will drain the Jeep's battery and get stranded up on a mountain somewhere. The solar system and LiFePO4 battery it's connected to are completely separate from the Jeep's electrical system.

Here are some pics of the solar panels installed. I like how low profile they are on the roof. I haven't had a chance to drive it on the highway yet so I will report back later about additional wind noise if any. The sun is not hitting them directly yet (pic looking east). Around mid day the sun will be above and to the drivers side (south), about as direct as you can get this time of year.

In case anyone is interested in the mounts, they are Audak tube clamps for bull bars and roll cages. A little pricey but super worth it. These things are strong. Here is the Amazon link:

https://www.amazon.com/Audak-Alumin...Adjustable/dp/B083JSVZ1V?ref_=ast_sto_dp&th=1

Here’s the stats at about noon today. Not bad for a couple of old 100 watt panels that are flat and not directly facing the sun! The battery will be fully charged by the end of the day. It’s cooking now at 10 amps!