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 Charger SC-120-12V
Aliexpress UK
Dual Battery Isolators also feature surge protection and a L.E.D indicator designed to alert the user when the unit is engaged. - Suitable for most 12V charging systems- Surge protection. When your engine is switched off, the relay will isolate your leisure battery(s) from your main starter battery.
eBay
PowMr 10A 12V Solar Charge Controller 12V Waterproof IP68 Without Light and Timer Control Load 24 hours Working Outdoor
Aliexpress UK
Dual Battery Isolators also feature surge protection and a L.E.D indicator designed to alert the user when the unit is engaged. - Suitable for most 12V charging systems- Surge protection. When your engine is switched off, the relay will isolate your leisure battery(s) from your main starter battery.
eBay
12 Slots 1.2V AA AAA Battery Charger Fast Charge Discharge Smart LCD Recharger for Ni-MH 1.2V Rechargeable Battery
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
12V to 110V/220V Solar Panel System 12V Solar Panel Battery Charge Controller 4000W Solar Inverter Kit Complete Power Generation
Aliexpress UK
Built-in LED indication (lights up when VSR starts). Automatically combines two batteries when charging and isolates the two batteries when not charging,which can widely used in 12v camper van trucks, caravans, and camping applications.
eBay
PowMr MPPT Solar Charge Controller 60A 12V/24V/36V/48V Auto Backlight LCD Display Solar Panel Regulator and Max PV Input 160Vdc
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
MYAMi 2800W MPPT Set-Down To 12V 24V 48V 50A 100A Off-grid Solar Charge Controller Caravan Solar System
Aliexpress UK
Dual Battery Isolators also feature surge protection and a L.E.D indicator designed to alert the user when the unit is engaged. - Suitable for most 12V charging systems- Surge protection. When your engine is switched off, the relay will isolate your leisure battery(s) from your main starter battery.
eBay
LED Voltage Display MPPT Wind Turbine Charge Controller Booster IP65 12V 24V 48V Voltage Regulator For 600W 800W Generator
Aliexpress UK
Dual Battery Isolators also feature surge protection and a L.E.D indicator designed to alert the user when the unit is engaged. When your engine is switched off, the relay will isolate your leisure battery(s) from your main starter battery.
eBay
20A 12V/24V MPPT Wireless Solar Charge Controller, Bateria Power Intelligent Solar Panel Regulator 20 Amp BT APP
Aliexpress UK