You can charge your batteries from your vehicles alternator. The alternator delivers power to all the vehicles electrical components and keeps the starter battery charged. The vehicles alternator may deliver more than 180 amps. Let’s say that 80 amps are needed for the vehicle that leaves a surplus of 100 amps. Those 100 amps can be used to charge your lithium batteries.
To charge from the alternator you need an Isolator, or Charging relay. These devices combine the starter and lithium batteries together.
A BIM, or battery isolation manager monitors voltage and connects batteries when needed. It will connect for 15 minutes, disconnect for 20 minutes, and repeat this cycle until the coach battery is charged.
If the coach battery resting voltage exceeds 13.4 V then the BIM will disconnect. A resting voltage greater than 13.4 V indicates a fully charged battery. The BIM will disconnect if the alternator voltage exceeds 14.4 V. This protects the coach battery from over charging.