When your engine is switched off, the relay will isolate your leisure battery(s) from your main starter battery. So it does not drain your main starter battery and you will always be able to start your vehicle.
eBay
Automotive 5 Pin Relay 80A Car 5 Pin 12V 80A Relay DC 12V 80A AMP Split Charge 5 Pin Car Vehicle Automotive Van Boat Truck Relay
Aliexpress UK
When your engine is switched off, the relay will isolate your leisure battery(s) from your main starter battery. So it does not drain your main starter battery and you will always be able to start your vehicle.
eBay
1Pcs Relay VSR for Camper Car Smart Battery Isolator 12V 140A Voltage Sensitive Split Charge for Car RV ATV Yacht
Aliexpress UK
When your engine is switched off, the relay will isolate your leisure battery(s) from your main starter battery. So it does not drain your main starter battery and you will always be able to start your vehicle.
eBay
1PC 12V 200 Amp Heavy Duty Split Charge/Winch Relay for Car Van Boat 4 Pin 80*42*42mm
Aliexpress UK
When your engine is switched off, the relay will isolate your leisure battery(s) from your main starter battery. So it does not drain your main starter battery and you will always be able to start your vehicle.
eBay
EASUN Solar Charge Controller MPPT 60A 50A 40A 30A 20A 10A Solar Panel Solar Charge Regulator 12V 24V Battery PV Input 100VOC
Aliexpress UK
When your engine is switched off, the relay will isolate your leisure battery(s) from your main starter battery. So it does not drain your main starter battery and you will always be able to start your vehicle.
eBay
40A MPPT Solar Charge Controller 12V 24V Battery Voltage Max Solar Panel 100V EPEVER Regulator With MT52 Data Monitor
Aliexpress UK
A VSR is a relay that separates the car's main cranking battery and the secondary accessories battery. The VSR is triggered by detecting when the alternator is running and charging the car battery. When the VSR detects that the car is on, it says "Hey the car's on!
eBay
DC 12V 24V 100A 200A WM686 Universal Relay 4 Pin Normal Open Car Starter Relay for Battery ON/Off Split Charge Relay Switch
Aliexpress UK
When your engine is switched off, the relay will isolate your leisure battery(s) from your main starter battery. So it does not drain your main starter battery and you will always be able to start your vehicle.
eBay
CNSPEED Smart Dual Battery Isolator 12V 140A Voltage Sensitive Relay VSR Split Charge with Digital Voltmeter For Camper Car RV
Aliexpress UK
When your engine is switched off, the relay will isolate your leisure battery(s) from your main starter battery. So it does not drain your main starter battery and you will always be able to start your vehicle.
eBay
MZMW UPS/Charge Function Switching Power Supply SC-35W 60W 120W 180W 12V 24V Monitor 110/220v AC/DC Battery Charge SC-120-12V
Aliexpress UK