In addition to the jump box, I rigged up my LifePo4 aux battery so that on occasion, if needed, I can switch my aux battery to charge my engine battery.? I made a simple drawing, attached.? Remember that if you add a lithium battery as your aux, you'll need to add a DC-DC charger (for LifePo4) and convert your AC-DC Charger as well.? All of it works great with solar and with a 1000-watt inverter! (not shown) Never leave your two batteries directly connected after your jump!
Bob H