Charging Travel Trailer Lithium batteries question

[Buyer2021]

I'd have to look at my notes from the time. Can't say for sure but if I hadn't turned off the solar, it would have only been 200W max at the time.

If your 200W solar array was connected to the battery via an MPPT controller on a sunny day, it's charging contribution to the battery in Amps could have been meaningful, thereby reducing the Amps demand from the truck.

Just mentioning because your test data may not reflect the Amps load a trailer's LiFePO4 battery bank at a low SOC could place on the truck's system absent concurrent solar charging.

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[Davexxxx]

If your 200W solar array was connected to the battery via an MPPT controller on a sunny day, it's charging contribution to the battery in Amps could have been meaningful, thereby reducing the Amps demand from the truck.

Just mentioning because your test data may not reflect the Amps load a trailer's LiFePO4 battery bank at a low SOC could place on the truck's system absent concurrent solar charging.

True and again, I'd have to check my notes but I do recall dropping SOC down to at least 60%. At that stage, a 600ah bank, would take everything a 200W solar panel could give it and lots more. The maximum I saw it draw from the truck was 8A.

 

[Calson]

A charger for lithium batteries should have a lithium setting. I have bought special chargers for my RV's to handle lithium batteries. The diesel generator in my motorhome also had a lithium setting and with a higher charge level the run times were much shorter than they would be for a lead acid battery.

With solar panels the batteries are being topped off even when the trailer is being stored or when at a campsite so no need to stay only where shorepower is available and so one has the option of dry camping. With my truck camper and my motorhome they main advantage to using them was to be able to dry camp. Otherwise we could save money by staying at a B&B or hotel.

 

[HammaMan]

Having a solar panel of any size is a must for keeping batts healthy. For extended periods, make sure it's not over-charging. Store LFPs below 70%. You don't want a situation where every "unused" day the solar panel top charges the batts and leaves them sitting there.

Solar is cheap and free energy sans lugging the panels around. Even w/ a PB, I'd still rely on solar as much as possible. Too cheap not to.

 

[Davexxxx]

Just out of curiosity, I double checked something and found a mistake. I thought I'd read somewhere on this forum, that the circuit for trailer battery charging is 10A. According to the generic 2023, F150 owner's manual, it is fuse #107 under the hood and is 30A, called "Trailer tow battery charge".

There is also an 5A fuse in the cab fuse box, #22, called "Trailer battery charge run / start". (Whatever the hell that means.)

It doesn't change the fact that I only read a max of 8A going to the trailer but it does indicate there is a healthy bit of headroom, on that circuit, on my system.

 

[HammaMan]

Yeah, the trailer tow/charge is a 30a, but the run is such that by the time it gets to the trailer, it's a trickle of a charge if there isn't a boost converter. Not going to get much of a charge w/ 30' of wire on a 12ga circuit.

 

[RickBullotta]

7 pin is at best a trickle charger.

 

[Buyer2021]

So far, I've found my 800W PV array / Victron MPPT 150/60 -TR Charge Controller keeps my 400Ah LiFePO4 battery happy without any charging from the vehicle (I disconnected the battery charge wire in the 7-pin umbilical cord junction box of my trailer, altering nothing on the truck because I have another trailer with a regular AGM battery and no solar).

I very rarely use shore power when camping, relying on solar and a Xantrex Freedom XC 2000 all-in-one inverter/converter/TS for my relatively modest AC and DC power needs. The Xantrex is analogous to a Victron Multiplus with fewer bells-and-whistles that I don't need.

I have a master disconnect which allows total isolation of the battery from all trailer charging and loads when parked for an extended period - the SOC drop of the isolated LiFePO4 is de minimis when sitting unused for even very extended periods. I have the trailer always connected to 30A shore power at the house when sitting this way to provide AC and DC juice for lights, refrigeration, and heating via the Xantrex whenever wanted.

I monitor my battery condition with a Victron BMV-712 / shunt.

This works well for my use-habits, but YMMV.

 

[Cobraman428]

I have 600ah of LiFePO4 in the camper and made no modifications to either vehicle, re the 7 pin.

I tested it at various states of charge and the most I saw it draw from the truck was 8A. I believe that circuit is protected by a 10A fuse?

I considered it a non issue and ~6K towing miles, hasn't given an indication that it was a bad decision.

However, on a non PB, I'd go with a DC to DC charger.

I just got a new lithium battery for my camper and I'm replacing the AGM batteries in it next week. So, with your PB you didn't do anything to the truck side and still no problems. I see that your post is a few months old now, any issues since you posted? I was concern about the charging and back feeding from the camper with solar controller to the truck. I just wanted to make sure I didn't need anything else. My camper has a LFP solar controller and the camper has a LFP converter so on my camper side I'm setup for LFP charging profiles. I read that you can burn up the alternator in the truck. I know the PB is a different beast with the HV battery. Just wanted to get some feedback from the group. Thanks!

 

[BILDOZER]

I have towed with the 2021 Lariat 2.7 and now the 2025 K.R. Powerboost charging two 100 amp hour lithium batteries an dhaven't killed the alternators or any other ill effects running the 12 volt fridge in route with no issues. I always charge the batteries at home and have seen over the years that with the 12 volt fridge running I arrive at the campsite with @ 90 to 95% state of charge. If your looking to charge your batteries from say 30%, get the Victron boost converter and upgrade the charge wirrring to the 7 pin connector otherwise the truck will only trickle charge as others said @ 10 amps which is barely enough to run the fridge and nay a stary amp or so going to the batteries.

I had a Winnebago Travato prior to 2021 and I litterally swapped the two 100 amp AGM's for two 100 amp China special lithiums and had no issues for 5 years. The alternator didnt blow up or burn out and Progressive Dynamics converter (non lithium)charged the lithiums in bulk mode at 14.2 volts with no issues to 95% or 13.3 volts resting consitently. The only mod I did was change the solar (200 wattes) controler to match the lithium charge profile. so most days drycamping left me at 100% S.O.C. at sunset.

My personal advice would be don't sweat it and enjoy the camping. Your truck nor your camper or the batteries will blow up or die if you leave everthing stock. You can through a couole thousand to obtain Lithium "Nervana" to always charge to 100% always starring at the Victron smart shunt monitor or enjoy the friends and the camping... My choice is the later.

 

[Davexxxx]

I just got a new lithium battery for my camper and I'm replacing the AGM batteries in it next week. So, with your PB you didn't do anything to the truck side and still no problems. I see that your post is a few months old now, any issues since you posted? I was concern about the charging and back feeding from the camper with solar controller to the truck. I just wanted to make sure I didn't need anything else. My camper has a LFP solar controller and the camper has a LFP converter so on my camper side I'm setup for LFP charging profiles. I read that you can burn up the alternator in the truck. I know the PB is a different beast with the HV battery. Just wanted to get some feedback from the group. Thanks!

About 7K miles now towing, no issues.

 

[if150]

It seems like the consensus here is to not worry about a DC to Dc charger from truck to travel trailer with Litium batteries. I just found this thread in doing my research as I try to upgrade my travel trailer for boondocking. Right now I have 400watts of solar and a flooded battery which runs the 12v fridge/lights/water pump/fan, but it’s about drained after one hot night. I’m looking to go with 200amp/hr life4po batteries but got concerned about the 7pin connector and not charging while driving (or ruining something on the truck).

So is a DC to DC charger unnecessary for a non PB truck?

Any recs or guides on wiring one in?

 

[Davexxxx]

It seems like the consensus here is to not worry about a DC to Dc charger from truck to travel trailer with Litium batteries. I just found this thread in doing my research as I try to upgrade my travel trailer for boondocking. Right now I have 400watts of solar and a flooded battery which runs the 12v fridge/lights/water pump/fan, but it’s about drained after one hot night. I’m looking to go with 200amp/hr life4po batteries but got concerned about the 7pin connector and not charging while driving (or ruining something on the truck).

So is a DC to DC charger unnecessary for a non PB truck?

Any recs or guides on wiring one in?

Since finishing a recent trip, I have about 10K towing miles on the 600ah LiFePO4 upgrade we did to our trailer. I can't tell you a single thing that has gone wrong with leaving the 7 pin in tact and taking whatever change it provides, with the caveat of always disconnecting the 7 pin, once the travel day is over.

But thats on a PB. I don't know what alternators, fusing, or wiring are on other trucks. I tested mine and was satisfied it would be ok and so far, haven't regretted it.

Having the 7.2 KW, is a pretty big security blanket. It can run the whole trailer and recharge the batts.

Without that, I'd use a DC to DC charger, the bigger the better. Victron has a new 50A version.

Gives you a plan B and automatically wipes the worry, warranted or not, of a problem of the LiFePO4s hurting your alternator.

 

[exploringcarolina]

Many folks use a DC to DC charger to charge their Lithium battery.

When I installed a single BattleBorn 100AH battery in our camper replacing two group 27 lead acid batteries, BattleBorn told me it was OK to let the 7 pin charge cable charge the battery while in transit for our installation, I recommend talking to the battery manufacturer.

If the Tow Vehicle's 7 pin charge pin remains hot with the TV ignition in the off position, it is possible to run the TV battery down with something operating in the camper with the TV 7 pin connected. We have a Victron BlueTooth shunt installed to monitor the battery and the TV charged the Lithium battery at about 3 amps.

Here's our single BattleBorn 100AH Lithium installed with water resistant Victron BlueTooth Shunt and Renogy solar controller with Lithium charging setting for our Renogy Solar Suitcase panel.

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