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.
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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
NJTY T02A AC Voltage Sensing Voltage Tester High Voltage Non-Contact Electric Pen Advanced AC
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
M18 8mm sensing DC 5V inductive proximity sensor switch NPN NO LJ18A3-8-Z/BX-5V work voltage 5VDC
Aliexpress UK
The relay is connected between the vehicles main battery (Positive) and the leisure battery (Positive). It simply connects between the two batteries. Permanent live output (a live feed via relay from main battery + generally never used).
eBay
LCTC 0-10V 4-20mA 0-5V SSR Solid State Relay Voltage Regulator Single Phase Slim Relay With Radiator
Aliexpress UK
The relay is connected between the vehicles main battery (Positive) and the leisure battery (Positive). Both input and output leads have 30 amp fuse holders. It simply connects between the two batteries.
eBay
Din Rail 3 Phase Voltage Relay 3P+N Voltmeter Ammeter Over and Under Voltage Monitor Relays
Aliexpress UK
140A Max rated at 14 volts. Max Current Load: 140A. Relay Closes (Makes) at 13.3v & Opens (Breaks) at 12.8v. Three simple connections - Primary Battery, Auxiliary Battery & Earth. Continuously monitors the charging rate of the alternator to make sure your leisure battery is maintained in optimum condition.
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GEYA GPS8-03 Din Rail 3 Phase Voltage Relay 3P+N Over and Under Voltage Monitor Relays Protector
Aliexpress UK
Built-in LED indication (lights up when VSR starts). 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
10Kw Voltage Stabilizer Single Phase 220V AC Regulator with LCD Display Relay Control Whole House
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
B16 Intelligent Sensing Digital Measuring Pen Non-Contact 30V-1000V Voltage Detector NCV Voltage
Aliexpress UK