It does this by taking a small current from the leisure battery. Battery guard cut-in:Starter battery below 11.5V. Battery guard cut-out:Leisure battery at 11.7V. Suitable for battery types:All types of lead-acid battery inc. wet, AGM, Gel.
Ablemail AMT12-2-PRO 12V Battery Maintainer - Suitable for Lithium Batteries
200PSI Air Compressor Fits 12V Vehicles Yacht Boats For Truck Car Train Horn 12V
12v Circuit Tester Load Tester Lamp Light 12v 55w H7 Bulb With 1m Test Leads
4,500lbs 12V Winch (PEW-12V-4500)
20A 12V/24V Smart Car Battery Charger Pulse Repair Lead-Acid & 12V Lifepo4
30A Smart Car Battery Charger Pulse Repair for 12V/24V Lead-Acid & 12V Lifepo4