I've got one of the Sterling 24v-to-12v battery-to-battery chargers. They certainly can be set for a lithium charging parameter.
Mine is mounted in the electrical bay near all my other gear like the inverter and solar charge controller. All you need to power it is an appropriately sized conductor running from the 24v battery bank to the Sterling, and then another appropriately sized conductor going to your house batteries. Mine will pull up to 35 amps from the 24v system and spit out up to 70 amps to the 12v house batteries.
You can set the Sterling up to charge whenever the bus's alternator is making power, but I set mine up to work on a manual switch. There are times I don't want to have it running, such as when I leave a campground and know that my batteries are fully charged. Like many multi-stage chargers, the Sterling will start at the bulk charging voltage and stay there for a while in the first stage, taking a while to reconcile itself with the actual state of charge of my batteries. But, when I've been boondocking I will turn it on right away as I start up the bus and by the time we're at the next stop the batteries are charged (or nearly so). Very helpful system.
