Using a lithium battery as a house battery in an overland vehicle

[jscherb]

I've been using marine deep cycle lead-acid batteries to power the fridge and campsite accessories in my two expedition Jeeps for a number of years and they've served me very well. I buy them at Walmart, they're under $100 and all but the last one I had lasted until the end of the three year warranty. In October 2022 the battery kitchen battery in my JKU started failing, it lasted 35 months, so I replaced it with another Walmart battery. They had changed the warranty to one year, which I didn't think that much about since I've had good luck with these batteries in the past. Apparently they really mean it, because the most recent battery failed in November 2023 after only 13 months. They probably changed the warranty because they apparently cheapened the battery. That story is a long way to getting around to saying I've been thinking maybe I should switch to lithium batteries or switch to deep-cycle batteries of better quality not from Walmart. Side note: why have I always bought them from Walmart? Because wherever I am in the country, if a battery fails while on a trip or expedition, there's always a Walmart somewhere to get a warranty replacement. And they're reasonably priced if I have to buy a new one out of warranty.

By a strange coincidence, at the same time I deciding to replace that last lead-acid battery, Lightning New Energy contacted me, wondering if I would be interested in testing their new lithium battery. Perfect timing, so I agreed and they sent me one to test.

Their lithium battery arrived in January:

The battery is 12V, 100Ah and uses LiFePO4 chemistry (Lithium Iron phosphate). LiFePO4 batteries are a type of lithium ion rechargeable batteries, their benefits over the more traditional cobalt-based lithium-ion batteries are increased power output, faster charging, reduced weight and longer lifetime.

I've been experimenting with the battery since it arrived and the following posts document the result of my testing and research on using Lithium batteries.

 

[jscherb]

Some explanation of the expedition electrical systems in my Jeeps is in order before getting more into the details of the battery. I'll start with terminology - several terms are used to describe second batteries in expedition vehicles, for this article I'll use the term house battery for the second battery. They're also called auxiliary batteries, kitchen batteries and several other names, but since this battery powers things used for the campsite, house battery seems like a good term to use.

The house battery is carried in a tray over the inner rear fender; in the '13 JKU, the tray is a MORryde ammo can/battery tray (https://www.morryde.com/products/ammo-can-battery-tray-kit-with-molle-holder/); there's a cover made from soft top fabric with MOLLE attachments on it for accessories:

In the '06 LJ I have a battery tray that mounts in the rear on top of the inner fender:

In both Jeeps the battery is in a battery box; I don't use the battery box cover because I use the fabric covers with MOLLE grids on them and I attach pouches to the MOLLE for storing battery/solar wiring accessories.

The house battery is charged by the vehicle alternator when the engine is running. When the engine is not running, there's no connection between the house battery and the main electrical system of the Jeep so the house accessories can never drain the starting battery when at a campsite. The charging connection is protected by a 50-amp circuit breaker; extensive testing has shown that the most the lead-acid battery will draw when discharged is just over 40 amps - this is something to be tested with the lithium battery, because some lithium batteries can draw much more when charging.

The house battery is also charged by a 100-watt solar panel. Outputting about 6 amps in full sunlight, the solar panel is enough to keep up with the drain of the accessories connected to it in most situations, which enables the Jeep to operate at a campsite indefinitely without resorting to the starting battery to power campsite accessories.

The solar panel is mounted to a slide underneath the roof rack and is pulled out at the campsite. In the event the slide-out panel can't be positioned for optimal sunlight, the panel is also removable from the slides and has legs, so with an extension cable it can be positioned somewhere on the ground and aimed at the sun.

The panel is a Harbor Freight monocrystaline unit that retails for $119.99, and is often available for less with a coupon (https://www.harborfreight.com/100-watt-monocrystalline-solar-panel-57325.html). I consider it an excellent value when compared to the price of other 100-watt panels. I also use their 100-watt solar charge controller which retails for $19.99, also an excellent value and completely adequate for this application (https://www.harborfreight.com/7-amp-solar-charge-regulator-96728.html). The HF controller is a PWM unit (pulse width modulation) and while there are more efficient charge controllers on the market (some known as MPPT controllers), I've found the HF unit to work just fine and keep up with the load on my house battery in almost all situations, and a $20 it's cheap enough to carry a spare. For the record: I've been using the HF controller for years and it's never failed so I probably don't need to carry a spare but for $20 ($16 with a coupon) why not.

And finally, so the house battery can be used to start the Jeep in the event of a main battery failure, a dash switch connects the house battery to the main battery for starting. Photos of that switch in the JKU (the switch is just above the suspension pressure gauge):

And in the LJ I've installed a switch to match the factory switches:

There's a power panel at the rear of the Jeep with several power and USB sockets. One of the power sockets is a screw type because I've found that type more reliable than the "cigarette lighter" type for the higher power draw of the refrigerator and the other two sockets are the "cigarette lighter" type.

A look at the full kitchen. Powered items in this view are the refrigerator and the sink pump.

In addition there's a direct connection to the battery with an Anderson SB50 connector, this is used to power a 750 watt inverter for running A/C accessories at the campsite. The inverter lives behind the MOLLE panel under the battery.

The description above should suffice to illustrate the situation in which the new battery is being tested.

 

[jscherb]

As mentioned above, the batteries I've been using are Walmart Marine Deep Cycle batteries. They're Group 24, 101 amp hour capacity, measure 10.25 x 6.88 x 8.69 inches and weigh about 45 lbs. They sell for $89: https://www.walmart.com/ip/EverStar...ery-Group-Size-24DC-12-Volt-690-MCA/180350522

The new lithium battery is rated at 100 amp hours so its capacity is the same as the Walmart lead-acid battery. It weighs 25 lbs. which makes it 20 lbs, lighter than the lead-acid battery. It measures 13.25" W x 7.25" D x 8.46" H, so about 3 inches longer than a typical Group 24 lead-acid battery but roughly the same depth and height. The advertised service life is 10 years, which is far superior to the 13 months I experienced with the current generation of Walmart battery or even 3 years which is more typical for a lead-acid battery. The advertised price of the lithium battery as I write this is $249 (https://lightning-energy.cn/product/gokwh-12v-100ah-lifepo4-battery-monitor-with-lcd-display/) which is roughly 3x the price of the Walmart battery but if the 10 year life is true, that's a much better value than the Walmart lead-acid battery.

Two other features of the lithium battery are that it has an integrated battery management system (BMS) and an LCD display.

The battery management system features include overcharge protection, output overcurrent protection and thermal management. All of those features are important, but the last one especially so - while LifePO4 lithium batteries are the safest of the lithium batteries because they're much less likely to experience thermal runaway, the BMS monitors battery temperature in real time to prevent thermal problems.

The LCD display is also very useful - it displays current battery voltage and remaining capacity and it has a user-configurable low-voltage alarm so you can be notified to take action if necessary when the battery reaches a preset voltage.

I removed the old battery and swapped the lithium battery in its place. The lithium battery has 8mm threaded holes for the terminals and connections to the battery are secure with bolts in those holes. With the old battery I was using marine battery connectors which have threaded studs and wing nuts, so it was easy to transfer the connections from the old battery to the new battery.

The integrated LCD display was showing 78% capacity, so the first thing I did was start the Jeep to charge the battery. The lead-acid battery would charge quickly with my configuration, but the lithium battery did not charge, which led me to research charging parameters for LiFePO4 batteries. According to the documentation that came with the battery:

LiFePO4 Batteries perform a 2-stage charging algorithm called "Constant Current/Constant Voltage" (CC/CV). The standard LiFePO4 profile is 2.2C CC charge to 14.2V, and then, CV at 14.4V charge until the charge current declines to <=0.05C. The recommended max. charging current for a 100Ah LiFePO4 battery is 50A. A faster charge of 100A may be used as necessary, however, regularly charging your battery this way may shorten its life and subsequently it s total capacity due to the extra heat generated during this process. We do not recommend using any other types of chargers for LiFePO4 batteries, such as SLA and Gel.

What that all means is that charging the battery from an alternator without any management of the current and voltage specific to the needs of the lithium battery is not recommended.

Most ordinary battery chargers (including the one I've used for years to charge lead-acid batteries) will not properly charge a LiFePO4 battery (and are not recommended as quoted above), so to continue the testing for now without upgrading the wiring in the Jeep, I bought a battery charger intended for marine use from Amazon. It's a NOCO Genius 10-amp charger maintainer that automatically detects the battery type - lead-acid, AGM or lithium.

While the battery was charging with the new charger, I ran a test on the lead-acid for comparison purposes. Sitting in the 40-degree garage (this was in January), the lead-acid powered the fridge for about 3 1/2 days until the voltage was low enough that the fridge shut down.

Even though the amp-hour rating of both batteries is the same (101AH for the Walmart battery and 100AH for the lithium) I expected a bit longer performance from the lithium. Here's why... according to battery company Power Sonic, lithium batteries deliver the same amount of power throughout the discharge cycle, but lead-acid power delivery decreases through the cycle. They provide this graph to illustrate that on their web site (https://www.power-sonic.com/blog/lithium-vs-lead-acid-batteries/).

I reinstalled the fully charged lithium battery in the Jeep and ran the same test and got a little over 4 days before the fridge shut down, which roughly confirms the graph above. I say "roughly" because over the time both tests were being run, the temperature in the garage varied a bit, which meant that the run time of the fridge in both tests would have been slightly different to keep the fridge cool given the ambient temperature changes, but the temperatures didn't vary greatly so I'm comfortable saying the lithium battery lasted longer.

 

[jscherb]

Now to figure out how to charge the lithium battery with the alternator...

The wiring from my starting battery back to my house battery is about 16 feet of CCA (copper clad aluminum) wire running both directions (positive and negative). The wire is from a set of jumper cables for this purpose, I cut off the clamp ends, cut the wire to the proper length, put appropriate ring terminals on the ends and ran it from the engine compartment to the rear of the Jeep. It's worked great for years and has kept the lead-acid house battery charged just fine.

CCA wire does not conduct as well as pure copper, but even with the voltage loss at charging current levels the voltage available at the back to charge the house battery is about 13.5 volts - plenty to keep a lead-acid battery charged. But not enough to charge a LiFePO4 battery, which require at least 14.4 volts. I did voltage loss calculations for pure copper wire, and the results of the calculations show that replacing the CCA wire with 2-gauge pure copper would reduce the voltage drop enough to provide adequate initial charging voltage.

The problem is that the recommended charging profile for LiFePO4 is multi-stage as I quoted from the battery manual earlier. Without additional circuitry, a stock vehicle alternator system almost certainly won't provide the charging profile.

The solution to this is a DC-DC charger which supports lithium batteries. These accept vehicle voltage and regulate the charging output to the needs of a lithium battery. One example is the Renology 12V 20A DC to DC On-Board Battery Charger: https://www.renogy.com/12v-20a-dc-to-dc-on-board-battery-charger/. It is compatible with AGM, Flooded, Gel, and Lithium batteries and uses 3-stage charging-bulk, boost, and float to ensure charge to 100%. As I write this, it's priced at $109.99, which seems like a pretty good value.

Summary: if your house battery is some distance from the alternator, an upgrade to serious gauge pure copper wires is in order, plus a lithium-compatible DC-DC charge controller between the alternator and the lithium battery.

So that will provide for charging the lithium battery properly from the alternator, but what about charging it from the solar panel? As I wrote earlier, I'm my vehicles the Harbor Freight 100-watt solar panel and $20 charge controller work jut fine to keep the lead-acid battery charged, but won't charge the lithium battery.

A lithium-compatible solar controller is necessary. One example is Victron's SmartSolar MPPT 75/15 Solar Charge Controller: https://dakotalithium.com/product/victron-smartsolar-mppt-75-15-solar-charge-controller/. It's recommended for use with 100-watt solar panels as a minimum, which would be fine for the Harbor Freight panel that I use. As I write this it is for sale for $119 at the Dakota Lithium web site, which also seems like a good value.

 

[jscherb]

So while I'm deciding if I want to make those electrical upgrades to my system (2ga copper wires, DC-DC lithium charge controller, lithium-compatible solar controller), I've found another use for the lithium battery - perhaps temporary until/if I decide to upgrade the components in the Jeeps - powering the battery backup sump pump in our new house (the house is actually very old - built circa 1815). The house has an AC-operated sump pump, but I wanted to have confidence that the sump wouldn't be a problem in a bad rainstorm with a power failure so I picked up a Basement Watchdog battery operated backup pump. It comes with everything except a deep-cycle lead-acid battery, so for now, rather than buy a battery, I'm using the lithium battery. If/when I decide to use the lithium battery in the Jeep(s), I'll move the lead-acid battery from one of the Jeeps into the basement to operate the sump pump.

Of course the electronics supplied with the Basement Watchdog won't charge a lithium battery, so I'm using the NoCo charger I wrote about earlier. Another thing the Watchdog electronics do is set the run time for the pump - once the float rises high enough to turn on the pump, the pump needs to run for a fixed period of time to drain the sump. If it ran only until the water level dropped enough for the float to lower and shut off the power, it would drain maybe a half inch of the water in the sump. I picked up a delay controller from one of my favorite electronics surplus places and connected it between the float switch and the pump relay; it allows me to set the run time from 0-99 seconds or 0-99 minutes. Here's a photo of battery and necessary wiring and circuitry, I need to organize the wires a little better after I finish testing it; right now I've got it set to run the pump for 45 seconds each time the water level rises enough to lift the float switch...

So for now I've got peace of mind that if the power fails and lots of rain raises the groundwater level, my sump won't overflow and the lithium battery should power the pump days longer than any power outage might last.

 

[jscherb]

I should spend a little time on what this battery is not - it's not intended to be the primary starting battery - the maximum recommended output current of the battery is 100amps, which is plenty for a house battery but well below what almost all automotive starters draw. It's also not recommended to expose it the to high heat of an engine compartment. Lithium batteries that can meet those specs sell for $850 to $1000 and more; this one is just $250.

So what about the feature in my Jeeps that allows me to start the Jeep from the house battery at the flip of a switch in the event the main battery fails or doesn't have enough power to start the Jeep? I asked the company about this and they really couldn't recommend trying to start the Jeep with the lithium battery - in high current output situations the integrated battery management system (BMS) would shut down the output to protect the battery.

So if you're in the wild and your starting battery is completely dead, this lithium battery probably won't start the vehicle. In my experience though, the most common failure mode for a lead-acid battery is a weak cell, causing the battery to only be able to deliver a portion of it's rated starting current, often not enough to start the vehicle even though the lights, radio, etc. will still be working. In those situations, this lithium in combination with the weak lead-adid may be able to start the vehicle without the BMS shutting the lithium battery down.

There are lithium batteries that do have the capability to start a vehicle, but they generally cost around $1000 each, which is more than 4 times what this lithium battery costs, so you get what you pay for I guess.


So far and in spite of the wiring and electronics changes that will be necessary to make it work in an overland vehicle, I'm impressed with the battery. Physically it was a direct swap for my lead-acid other than being a few inches longer (I had the extra space), it was about half the weight of a lead-acid, it powers the fridge and other camping equipment longer, it has a stated service life of 10 years and at the current price ($250), it's not that much more expensive than a high quality deep cycle lead-acid battery if you don't factor in the cost of the additional electronics required.

Here's more info on the complete line of LiFePO4 batteries from Lightning Energy: https://lightning-energy.cn/product-category/lifepo4-battery/, including Bluetooth versions that provide monitoring battery status from your cell phone.


If I decide to upgrade my wiring and electronics to support this battery in one or both of my Jeeps, I'll post the details but in the meantime the battery is providing my with peace of mind serving as the power for the backup sump pump in my new house.

 

[nwoods]

I always learn so much from your posts. I am so appreciative of your contributions here on ExPo!
I have a somewhat related question to your battery topic: What is that vented cage tucked into your JK fender wall that your battery pack tray is sitting on? Is that something you designed that is available for sale somewhere?

 

[jscherb]

I always learn so much from your posts. I am so appreciative of your contributions here on ExPo!
I have a somewhat related question to your battery topic: What is that vented cage tucked into your JK fender wall that your battery pack tray is sitting on? Is that something you designed that is available for sale somewhere?

Thanks for the kind words.

The tray holding the battery (or can hold an ammo can) and the MOLLE grid below it is something I designed; MORryde picked up the design: https://www.morryde.com/products/ammo-can-battery-tray-kit-with-molle-holder/. It fits on either side of the JKU.

 

[rruff]

Lightning New Energy contacted me, wondering if I would be interested in testing their new lithium battery. Perfect timing, so I agreed and they sent me one to test.

Ha! I got one in December. It works great, unlike the Power Queen I bought that failed to balance properly and was returned.

LiFePO4 is very normal chemistry for house batteries... really no other lithium is in the game.

 

[rruff]

Summary: if your house battery is some distance from the alternator, an upgrade to serious gauge pure copper wires is in order, plus a lithium-compatible DC-DC charge controller between the alternator and the lithium battery.

Surely the charge controller will negate the need for large wires, as it will adjust the output to what the battery needs...? I'm not familiar with the Renogy DC-DC though. I'm interested in how it works for you, as I'm thinking about getting one to supplement the solar.

 

[jscherb]

Surely the charge controller will negate the need for large wires, as it will adjust the output to what the battery needs...? I'm not familiar with the Renogy DC-DC though. I'm interested in how it works for you, as I'm thinking about getting one to supplement the solar.

The time it takes to fully charge the battery is a function of the voltage and the current input to the charge controller and the output the charge controller can provide with that input; the output of the charge controller will depend on adequate input voltage and current. You need to look at the specs to know the required input voltage and current for a device like the Renogy I posted above to output its full 20 amps of charge current and then calculate the appropriate size wire to deliver that voltage and current to the charge controller given the distance from the voltage source. There are voltage drop calculators online to help with this. Here's one example (https://www.grealpha.com/resources/dc-load-wiring-calculator/calc/voltage-drop/)... let's say the distance between your engine compartment and your house battery is 16 feet (that's what it is in my JKU), and you run 16-gauge wire to the charge controller, which is mounted in the back by the battery. Let's say the average output of your alternator is 13.5 volts. The voltage drop to the back will be over 2.5 volts at 20 amps, which means the charge controller will be getting 11 volts if it's drawing 20 amps. The specs for the charge controller need to be checked to see if it can output it's full rated 20amps charging current with only 11 volts input.

It's unlikely that 16-gauge wire will deliver the necessary voltage and current to the charge controller for it to provide its full output to the battery but the specs of the specific charge controller chosen will have to be checked to see what it needs as its input to provide full output.

That explanation is a bit simplified, but illustrates the need for proper gauge wire given the length of the run in order to provide adequate current for everything to work as expected.

BTW charging time is a function of the amp-hour rating of the battery and the charge current provided - the time it will take a 10-amp charger to charge a fully discharged 100 amp-hour lithium battery is roughly 100 ah / 10a = 10 hours. That's approximate, there can be other factors involved, but it's good for a rough estimate.

 

[NMNomad]

Thank you for the write up. As someone who is getting ready to install a dual battery setup, this is very useful information.

 

[jscherb]

Thank you for the write up. As someone who is getting ready to install a dual battery setup, this is very useful information.

I'm happy to provide any more details about the installations in my Jeeps or try to answer any other questions you might have.

 

[Zeep]

Welcome back! Hope your move went smoothly.

 

[Dan Grec]

Hey Jeff,
If you're going to upgrade your charging system, check this out

RENOGY 12V/24V IP67 50A DC-DC Battery Charger with MPPT

Renogy provides solar panels, charge controllers, inverters, lithium batteries, portable solar generators and other equipments for off grid solar power systems

www.renogy.com

It's a dual charger (DC-DC & Solar) that does everything you want.
I'm actually installing it in my Africa Jeep right now to ugrade the very outdated system. I'll have a video review out shortly.

-Dan