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
Relay Switch Controller DC 6~80V Voltage Detection Charging Discharge Monitor with Case Digital
Aliexpress UK
【Fit All types of Battery】 -- Fit for Lithium Battery, Lead-acid Battery, AGM Battery etc. 【Delay Setting Function】 —— The new delay function avoids frequent switching on and off of the isolator due to unstable current, which prolongs the isolator and battery life.
eBay
SSR 10VA 25VA 40VA Solid State Relay Voltage Regulator 24-380V AC Output with Potentiometer 10A 25A
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
Tuya eWeLink WiFi Smart Circuit Breaker MCB 1P+N 63A Time Relay Switch Energy Meter kWh Voltage
Aliexpress UK
It simply connects between the two batteries. The relay is connected between the vehicles main battery (Positive) and the leisure battery (Positive). The most important part of the circuit are the fuses!
eBay
2P 63A TUYA APP WiFi Smart Circuit Earth Leakage Over Under Voltage Protector Relay Device Switch
Aliexpress UK
5mtrs 110amp 16mm2 Red Power Cable. 1mtr 110amp 16mm2 Black Earth Cable. Including a 6-way Fuse box + 100amp negative bus bar to safely power your 12v electrics. 2 x Fuse holders & 100amp Fuses including spare.
eBay
2P 63A Tuya WiFi Smart Earth Leakage Over Under Voltage Protector Relay Device Switch Breaker Energy
Aliexpress UK
Here to give You the Best Experience. We have not authorised a signature release (for your parcel to be left anywhere, unsigned for). Clear Cut Campervan Design. Here to give you the. Clearcut Campervan Design Ltd was established over 15 years ago.
eBay
2P 63A TUYA APP WiFi Smart Circuit Earth Leakage Over Under Voltage Protector Relay Device Switch
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
A30-U3 DC Voltage Relay 6-80V48V60V 30A Detection Control Delay Switch Interval Action
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
Single-Phase Fully Isolated AC Voltage Regulating Module SCR Power Regulator Solid State Relay
Aliexpress UK