Different batteries for power

If you do it via a DCDC charger it cant be a problem.

Geoff
As QLD camper said, with a DC DC unit running off the Lithium to the Lead acid it will work with some loss of energy of course. You would have to ensure the drop out voltage of the DC DC unit isn't going to harm the Lithium though. Best to check what the lithium can safely deplete to in voltage and if that matches the Dc Dc unit's startup and dropout voltage. DC DC units typically run off an alternator or solar source which is higher voltage than a static lithium. Because the batteries have vastly different characteristics of amp flow and voltage retention it would be unwise to simply connect a Lithium to an AGM or Start battery as you would have no control over the current flow from and into. Others will have more info of possible use too.

.
Hi Geoff,

Simply connecting the lithium battery directly to the lead-acid battery and its connected loads in the caravan will safely provide energy to those loads. It will not however provide a charge transfer to the caravan battery as the lithium voltage is insufficient. Use an adequate wire gauge for the link cable and fuse it at each end.

You would of course need to supervise the discharge voltage of the lithium just as you would if it was discharging into its own connected loads. And break the link between the two batteries during charging.

Thanks everyone who responded. It seems that a DC-DC charger with input regulator/discharge is the way to go. Orion Tr smart charger ordered.

Thanks Allan, But also wanted to regulate the level of discharge of the Lithium battery. They are too expensive to discharge too deeply too often.

As pointed out, beware the DCDC as it may see the higher Lithium battery terminal voltage as the alternator charging , in my case as soon as I plug the camper into the cars aux the Enerdrive DCDC starts charging the Lithiums in the van off the Lithium in the car.