Is DC-to-DC Charger Required To Use RV Lithium Battery LiFePO4 GP99QR?

Updated 02/26/2025 | Published 08/01/2021

Products Featured in This Question

Redarc In-Vehicle BCDC Battery Charger - Dual Input - DC to DC - 12V/24V - 25 Amp

(87)

$535.00

Go Power Sun Cycle Advanced Lithium RV Battery - LiFePo4 - Bluetooth - Group 24 - 12V - 100 Amp Hour

(2)

$999.99

Question:

I’ve read quite a few articles regarding the installation of a 100ah Lifepo4 battery on a toy hauler or trailer. I want to know do I have to have a dc-dc converter? I don’t mind if the trailer battery wouldn’t be fully charged upon arrival after a long drive. If the tow vehicle is supplying appx 13.8 volts through the 7 pin socket that should be enough to supply somewhere in the 80 SOC. I can fully charge it after I’m on location with either solar or shore power. So, is it a problem to only use the power straight from the 7 pin socket? The BMS board should also protect the battery but I don’t see where that will be a problem. I’m more concerned about damaging my Lifepo4 batteries than the amount of charge while underway. Thank you.

asked by: Don

Helpful Expert Reply:

You do not need to have a DC-to-DC charger like the Redarc # 331-BCDC1225D installed in your trailer to use the Lithium Battery # GP99QR you have.

You can hook the battery directly to the 12v power circuit of your tow vehicle, but this will not charge up the battery. It will only put a maintenance charge on the battery due to that circuit having so little of an amp rating.

Since you are not worried about having the battery being fully charge while towing, and will use solar or shore power to keep the battery charged then I would save the money and NOT get the charger. If you change your mind in the future then you can always add a charger like the # 331-BCDC1225D later down the road.

As long as you are not allowing the battery to go dead and leaving it that way for a while you will not have any issues.

expert reply by: Samuel C

Jon G.

2/26/2025

I am about to change over to lithium as well and A LOT of articles I am ready say that connecting the 7 pin without this can cause damage to the two vehicle alternator. Is this accurate?

Robin H.

2/26/2025

@JonG this comes up from time to time and as far as I know there isn't a conclusive answer. Some people run this setup without any additional parts and don't have any issues with their alternator. Others say it caused damage. I imagine there are a lot of factors such as what is the vehicle, are the batteries completely depleted or mostly charged, and how much do you tow that play into this. Regardless, if you want to actually charge the battery then you need the # 331-BCDC1225D. If you're worried about damage then it is best to be safe and install it anyway