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
TOMZN TOVPD3-63VA Din Rail 3 Phase Adjustable Over and Under Voltage Protector relay with current protection 3*220V 380V
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 Voltage Detection Relay Module Circuit Monitoring Module Overvoltage Protection Discharge Monitoring Board
Aliexpress UK
Suitable for most 12V charging systems- Surge protection. 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
LANBOO 6mm Ultra thin design type Relay with Led 6A DC12 24V Microrelay Intermediat Other voltages can be customized e 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 Charging Discharge Monitor
Aliexpress UK
Allows split charging of second battery bank without discharging the primary/start battery, relay makes at 13.7 volts and breaks at 12.8 volt. 12 volt 160 amp. We operate a dispatch policy to ensure your parcel will be processed within 24 hours.
eBay
Voltage relay Single-phase solid state relay Transparent shell plastic cover shell Small solid rail radiator seat SSR-40AA 25AA
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
ESP32 Relay Development Board AC/DC Power Supply Voltage Monitor WiFi Bluetooth BLE 4 Channel Wireless Control Relay Module
Aliexpress UK
For 12V Leisure Battery Capacity up to 220AH. Designed for dual battery systems. 1x VSR(with/without LED) with fitting hardwares. CE Certified. IATF16949-2016 Certified.
eBay
Car Relay Tester Voltage Tester ANENG RT01 Universal 11-25V Automotive Car Battery Check LED Indicator Light Relay Diagnostic
Aliexpress UK
Safety Certified: CE certified with built-in surge protection, ensuring safe and efficient energy transfer. -Flexible Mounting: Surface or panel installation options for hassle-free setup. Waterproof Level: IP67.
eBay
ANENG RT01 Universal Car Relay Tester Voltage Tester 11-25V ar Battery Automotive LED Indicator Light Relay Diagnostic Checker
Aliexpress UK