I have done that before. My main remote power supply is a 12v 2,000w samlex on top of 60ah of LiFePO4 prizmatic cells.
The lithium battery attached to the power inverter would supply the Lions share of power then the lead acid would provide 20-30 amps through jumper cables under load, then 10-15 amps during recharge.
Bus this was an ice car with a rather anemic alternator.
The samlex has a built in breaker that triggers if I connect a 9 inch grinder or skill saw with out a varriac.
2011 white SL leaf with 2014 batt.
Chargers: Panasonic brick moded for 240v, duosida 16a 240v and a 10kw setec portable CHAdeMO