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
DC 9V 12V 24V Voltage Detection Relay Module Circuit Monitoring Module Overvoltage Protection
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
TOMZN Din Rail Dual Display Adjustable Over Under Voltage Current Protective Device Protector 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
NEW Version! DC 12V 24V LED Digital Relay Switch Control Board Module Relay Module Voltage Detection
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
Voltage relay Single-phase solid state relay Transparent shell plastic cover shell Small solid rail
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
LCTC Solid State Relay SSR DIN Rail Slim Relay 15/25/40A 0-10V 0-5V 4-20MA Voltage Regultaor Thin
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
DC 9V 12V 24V Digital Voltage Control Relay Module Relay Switch Control Board Module LED Voltmeter
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
DC 6~80V Voltage Monitoring Relay Time Delay Relay Charging Discharge Controller Module Undervoltage
Aliexpress UK
Note: The benefit of this type of relay is that it does not require a connection to the alternator or any modifications to the existing vehicle electrical system. The location is very good.
eBay
16A AC230V DC110V 24V Dual Voltage Impulse Relay Household Electric Pulse Control Relay Auto Control
Aliexpress UK