How to Charge a Lead Acid Battery from Lithium Phos batteries?

David G

New Member
In my travel trailer I'm in the process of installing 3 105 A-hr LiFP batteries and a 3 KW Victron Multi-plus inverter charged from 500 W of PVs controlled by a Victron 100/50 MPPT. The LiFP batteries, ect. will be about 20 ft from the existing batteries up front. I'm wondering if it is possible to retain one of the lead acid batteries and charge this from the LiFP battery pack? This way I would isolate the LiFP circuit from the existing 12 V lead circuit which has some benefits such as smaller wire to the tongue jack and retain the converter and tow vehicle charging. I was looking at a Victron Orion 12 V to 12 V 30 amp device but it doesn't appear to really be a charger for Lead batteries. It could be made to work by adding a switch or relay but I want something simple and automatic. Also, it appears that the LiFP voltage will at times drop too low for Lead acid charging.

Should I just give up on this idea and buy heavier cable and add small voltage regulators for any sensitive devices...TV or example?

David G


Participation Medalist
I was looking at a Victron Orion 12 V to 12 V 30 amp device but it doesn't appear to really be a charger for Lead batteries.
I have experience with the Smart version of the Orion. It turns on automatically when it senses a higher voltage (from an alternator in my experience) and turns off automatically when voltage is back down to nominal.
What is your use case for the lead acid battery? Is this something that really just needs a trickle charge or will it have real loads and need a 30a charger?

FWIW, there is also a Victron Orion 18a charger that for some reason is a little "less advertised".

David G

New Member
Thanks Sandals, The idea was to keep the LA charged from the tow vehicle or the on-board converter when plugged in so I would have normal 12 V power for the trailer DC uses, mostly minor. The LiFP batteries would only power the inverter and dump some power to the LA battery. I think I will just stick with the LiFeP batteries and delete the heavy LA batteries and disconnect the tow vehicle DC power to the trailer. If I have voltage issues with some on-board equipment (fans or TV) I can always add an inexpensive regulator or run my Victron 18 Amp AC to DC charger off of the inverter to charge the LA batteries.

David G


Solar Addict
If your needs are minor, such as just maintenance for a large Pb, or charging small batts in a trailer from/for Pb or LFP, there is something I've used in a pinch out in nowhere land that comes mostly from the Motorcycle application:

It's funny to be working with two sets of clamps, but at least it's smart enough not to kill the donor battery and will shut down if need be.

Pretty sure it's not what you're looking for, but nice to know. Bright orange so you don't lose it in the weeds. :)