Can you add a lithium battery to your camper for boondocking without pulling out the lead-acid battery? Yes, with a couple things to be aware of.

I added a 12V 100Ah lithium battery inside my travel trailer and left the original lead-acid battery right where it was on the tongue. A cheap battery selector switch picks which one runs the camper. Here’s how I wired it and how it worked on a real trip.

What the battery on the tongue actually does

When you’re not plugged into shore power, the 12V system runs a lot of the trailer: the front jack, electric landing gear if you have it, and the emergency breakaway brakes. That’s the little cord next to your safety chains. If the trailer comes off the truck on the freeway, it pulls out and the battery applies the brakes.

It also feeds the breaker box, which sends power out to the lights, fans, some circuits on the fridge, the furnace and all kinds of other stuff. It’s kind of the heartbeat of the trailer.

Why I didn’t put the lithium on the tongue

I live in Kansas and it gets pretty cold here. I wouldn’t want lithium batteries sitting outside in storage. My camper’s kind of a princess. It stays inside the shop, and I don’t even winterize it because we camp pretty late into the year and pretty early in the year. This year we were camping in January. But if it lived in storage somewhere that’s not my house, you’d probably want to take your expensive lithium batteries out.

That’s where the brakes come in. If your only battery is lithium on the tongue and you pull it for storage, you might not have breakaway brakes anymore. Then you go to tow it, it comes unhooked from the truck, and it’s not going to apply the brakes.

Theft is the other concern. A battery on the tongue is easy to walk off with.

The old battery is fine for what it does

I’ve been running this lead-acid battery for four or five years. It’s getting older and it’s a little weak, but there’s nothing wrong with it for the landing gear and brakes, and it’ll run the furnace for a while.

On that January trip the furnace sucked my batteries all the way down. If I couldn’t have gotten my generator started, I wouldn’t have had coffee, which is a bad thing. That’s a big part of what started this.

I like options. Different ways for power to come in, different ways for it to go out, and backups. So I wanted the new battery inside the camper, I wanted it removable, and I wanted to change as little as possible to get it working right.

How it’s wired

My trailer is a 2015 Jayco Jay Flight 26BHS with the stock WFCO setup. The lead-acid battery runs the jack and the brakes directly, through a couple circuit breakers, before it ever goes through the converter. A separate wire goes from the battery over to the breaker box and feeds the rest of the rig.

I interrupted that one wire, between the lead-acid battery and the breaker box. The lead-acid still powers all the chassis stuff, but it’s not touching the fridge, the furnace, the fans or the lights unless I pick it.

Then I added a 12V 100Ah lithium battery in the pantry and ran a wire behind the furnace over to it. The switch sits next to the breaker box with three wires on it: one from the lead-acid battery, one going to the panel and one going to the lithium battery.

The switch is a 1-OFF-2 battery selector, about $15. Position 1 is the lead-acid battery, 2 is the lithium, and OFF is off. Whichever one you pick runs the camper.

I literally finished this 10 minutes before a camping trip. The wires were a little bigger than I expected, so they’re showing for now. I might relocate the switch behind something later.

Get a switch with no BOTH position

This is the important part. A lot of battery disconnect switches are 1-OFF-2 plus a BOTH setting that connects the two batteries together. You don’t want that.

Say one battery is run down to around 10 volts and the other is sitting at 13.6. Connect them and you get a huge rush of power from one to the other. If you fused it properly you blow breakers. If you didn’t, you melt stuff, and that’s not good.

So I very specifically got a 1-OFF-2. There’s no setting where the lithium battery can connect to the lead-acid battery. Keep batteries of different chemistry on different circuits.

The battery, breaker and wire

The battery is a Vatrer 12V 100Ah LiFePO4. Full disclosure, Vatrer didn’t sponsor this. I won it in a big giveaway they did for 20-some people earlier this year.

It has a 100 amp BMS, which is more than this setup should ever see. My converter is rated at 55 amps, so I put a 60 amp resettable breaker on the battery. You can only get so precise.

I ran 4 gauge wire. The rest of the trailer is 6 gauge, but wire is really expensive and I had some 4 gauge, so I used what I had.

On the battery end there’s the breaker and a set of 120 amp Anderson-style quick disconnects, and everything’s heat shrunk. I put some stops on the pantry floor so the battery sits in there nice and tight. It’s as low as possible and as close to the axles as I could get it, tucked back in there with the pots and pans.

I can disconnect it and pull the battery out of the camper in about 30 seconds.

How I use it on a trip

I went on a camping trip a couple weeks ago and it worked flawless. I had the switch on 1 the whole time we were traveling and did everything just like I normally do. Got the camper level, used all my jacks, all of it.

Once we were all settled I flipped the switch over to 2. That’s how I ran the furnace through the night, plus the lights and everything else. It all worked out fantastic.

When we went home the next day I swapped it back to 1, but you really don’t have to. The lead-acid battery still runs the chassis stuff either way, and the truck trickle charges it a little bit through the trailer connector.

How the lithium battery gets charged

The factory converter charges it. The converter feeds the breaker box, so when I’m plugged into shore power with the switch on 2, it’s charging the lithium battery. Mine is the stock WFCO WF-8955PEC, and it has a 14.4 volt bulk charge mode that gets the lithium battery full just fine. I tested it myself.

Testing it with shore power unplugged

In the video I unplug shore power so it’s running on 12V only. On 1, the lead-acid battery, my little cigarette lighter voltmeter reads 12.6 volts, which is about fully charged. I ran the slide halfway out and it dropped to 12.5.

On OFF, everything shuts off. On 2, it’s running off the lithium battery and reads 12.8 volts.

Putting it back to stock

I can pull out the battery, swap the switch back to 1, and it’s like nothing ever happened. If I sell the camper I could legit leave the wire in the wall, disconnect my battery and be good to go. There’s some value to that in my opinion.

All of this is the 12V side. I’m not talking about the 110/120 volt stuff at all.

That’s really the whole setup: a switch, a breaker, some connectors and an extra battery. You just have to make sure you’re selecting one or the other. I’ll do a follow-up video once I’ve run it a while.

If you have any questions, ask them in the comments. I’m happy to help out.

More on my camper’s power

• My no-wiring lithium setup with a Pecron F3000
• Charging the trailer from the truck with the Pecron alternator charger

Stuff mentioned in this post

• Vatrer 12V 100Ah heated LiFePO4 battery
• 1-OFF-2 battery selector switch
• 60A resettable circuit breaker
• Anderson-style 120A quick disconnects
• Hydraulic battery cable crimper

Heads up: I won the battery in this post in a Vatrer giveaway. Vatrer didn’t sponsor it. The Amazon links are affiliate links.

As an Amazon Associate I earn from qualifying purchases.