Charging house batteries off of a vehicle's alternator (when the engine is running) is a fantastic way to provide a lot of charging to your house batteries very quickly. Even most smaller/older vehicle alternators are capable of putting out dozens of amps of current, which is especially useful for charging deeply discharged house batteries.

Depending on your house battery chemistry, there's a few different ways you can recharge your house batteries off of the alternator.

Usable only when your house battery is the exact same chemistry as your vehicle battery; usually this would require you having an FLA or SLA