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
21*18650 Battery Power Bank Case Battery Storage Box T21 Flashlight Wireless Quick Charge Dual USB DIY Shell 18650 Holder Box
Aliexpress UK
Designed to protect/insulate the base of your leisure battery. Black Plastic Full Battery Box. Dual USB Ports 12V/24V LED Interior Reading Light Caravan Boat Touch Switch New. 2x 12V USB Spot Touch Dimmable Lamp LED Reading Light for Campervan Caravan Boat.
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Lifepo4 Battery Box 12V 24V 48V 120ah 180ah 200ah 280ah Lifepo4 Batteri Box Camper RV Batteri Solar Cells Plastic Battery Case
Aliexpress UK
BITE ALARMS. BISON REAL LEATHER GOODS. BEACH TRIPODS. THREADED TUBES. SALMON FLY TUBES. TURBO CONES. GOLD HEADS. BEADS & TUBES.
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Solar Battery Storage Boxes For Garden/Lawn/Square LED Lamp Automatic Switch Rectangular Battery Box Household Accessories
Aliexpress UK
48mm Exhaust Pipe DB Killer Motorcycle Silencer Noise Sound Eliminator Silver. Waterproof Case for Go Pro Hero Hero 9/10/11/12 Black, Protective Underwater UK. Use with Electric Outboards, Trolling Motors and Recreational Boating.
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13S4P/13S5P/13S6P Nickel Plated Set for 18650 Hailong Battery Box 13S4P for 52 cells 21700 Polly Battery Box Nickel Sheet Sets
Aliexpress UK
Product Code: PO580. Supplied with strap. Plastic Battery Box with Lid.
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Lithium Battery Storage Box For Bosch 18V Li-ion Battery Plastics Case Charging Protection Circuit Board PCB Box Housings Shells
Aliexpress UK
Leisure Battery Box. With fastening strap. Yellow & White. The cover can be raised by 30 mm using the 4 x shims (included) so batteries upto 235 mm high can be accomodated.
eBay
2pcs/set 12V Battery Plastic Case Storage Box For Milwaukee 48-11-2411 M12 Li-ion Battery Box Housing Middle Shell Top Shell
Aliexpress UK
eBay
Full Set 48V 13S4P/13S5P/13S6P Nickel Plated for Hailong Battery Box 13S4P 52 Cells for Polly Battery Box 21700Nickel Sheet Sets
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
12V 24V 30Ah 40Ah 50Ah Lifepo4 Battery Storage Box 32650/33140 Lithium Battery Plastic Case Solar UPS Power Outdoor Power Box
Aliexpress UK