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
12V 140A Charging Relay, Dual Battery Smart Isolator Voltage Sensitive Relay VSR Waterproof with
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
Aliexpress UK
RV Window 500x300mm Horizontal Slide Camper Window Waterproof Round Corner. 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.
eBay
Relay Module WiFi 4‑Channel ESP8266 Development Board Voltage Monitoring Relay Industrial Parts for
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
LCTC 0-10V 4-20mA 0-5V SSR Solid State Relay Voltage Regulator Single Phase Slim Relay With Radiator
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
GEYA GPS8-03 Din Rail 3 Phase Voltage Relay 3P+N Over and Under Voltage Monitor Relays Protector
Aliexpress UK
We are an approved Durite UK Distributor. Allows split charging of second battery bank without discharging the primary/start battery, relay makes at 13.3 volts and breaks at 12.65 volt. 12 volt 140 amp.
eBay
Waterproof Automotive Relay 4 Pin 5 Pin 30A Auto Relay With Fuse Coil Voltage DC 12V/24V 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
LANBOO J13A Micro voltage plug-in relay 5pin 8pin 12vdc 12A relay AC 220v DC 24V universal relay
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.
eBay
TOMZN TOVPD3-63VA Din Rail 3 Phase Adjustable Over and Under Voltage Protector relay with current
Aliexpress UK