In order to design a system that will not abuse your alternator or batteries, it is important to know what kind of alternator charging system you have.

What you need:
Voltage meter capable of measuring DC voltage accurate to the tenth of a volt

What to do:
1. Locate your main vehicle starter battery
2. Start the engine, ensuring any fans, radio, lights etc. are turned off.
3. Take a voltage reading across the main vehicle battery
4. Leave running for around 5/10 minutes, then repeat step 3

If your readings are around 14.4V DC, then you most likely have the traditional, non-smart alternator.  This kind of alternator is ideally suited for one of the Victron Cyrix based systems listed below.
120A AGM
230A AGM
120A Lithium
230A Lithium
Tow Vehicle 7-pin adapter for AGM
Tow Vehicle 7-pin adapter for Lithium

If your reading is closer to 12.5-13.5V DC, or you know you have regenerative breaking, then it’s likely that you have a smart alternator, and will need an Orion or Sterling DC/DC charger alternator charger kit.

Warning:  This can be a very dangerous test to perform. Voltmeters have strong little wires and the battery is most easily tested right next to the engine belt system.  Be careful not let anything get near the belt.