DC-DC Chargers

If you’re using lithium batteries and want to charge them from your alternator, the best way to do it is with a DC-DC charger. It will protect both the alternator (and your cars electronics) and your lithium battery from overload conditions and wrong voltages.

Renogy 50

Amps: 50
Automatic On/Off: Yes
Charges starter battery: Yes
Smart Alternator Compatible: Unknown
Link: Amazon

This is Renogy’s latest DC-DC charger. What I like about this one is that it will automatically turn itself on and off based on incoming voltage from the alternator. There’s no need to run a separate wire to the ignition relay to act as an on/off switch. This unit also includes a 50-amp MPPT solar charge controller, which is a nice bonus for sure! Plus, it can trickle-charge your starter battery from the solar panels once your house battery is full. Seems like a perfect unit for most vans and motorhomes.

Renogy 40/20

Amps: 40 or 20
Automatic On/Off: Requires additional wire to the ignition relay
Smart Alternator Compatible: Yes
Charges starter battery: No
Link: Amazon

These units have some pros and cons compared to the Renogy 50 above. They’re isolated power systems, so you don’t have to mix grounding between battery types, which is nice. But they have a input terminal that requires voltage be delivered to it to activate the system. This can be done by connecting to the ignition relay, but that’s another wire that has to be run which complicates the install. These units are less expensive though, and can run at lower amperages, which can be good for trailer installs.

Victron

Amps: 30
Automatic On/Off: Yes
Smart Alternator Compatible: Yes
Charges starter battery: No
Link: Victron

This is a new unit from Victron, but checks all the boxes. Automatic on/off feature, isolated power, and even bluetooth connectivity. Rumors say it should be available January 2020 in the United States.

Sterling

Amps: 30 / 60
Automatic On/Off: Yes
Smart Alternator Compatible: Yes
Charges starter battery: No
Link: Amazon

Sterling has been around for a long time and is well known. Their DC-DC chargers are more expensive though, especially compared to the frugal Renogy products. Available in both 30 and 60 amp versions.