12V Battery Isolator Switch Voltage Sensitive Relay with 13.3V Cut-In 12.7V Cut-Out 5 Second Delay and 140A Continuous Rating

The MT005 is a voltage-controlled battery isolator designed for 12V DC dual-battery systems. It closes at a 13.3V cut-in threshold and opens again at 12.7V, holding the open state for a 5-second delay so a brief voltage dip under load does not split the battery banks unnecessarily.

In practice, this means the auxiliary battery is charged whenever the alternator or charger is working, and is separated from the starting battery once charging has finished and surface voltage has settled. The starting battery stays reserved for cranking — even if a fridge, lights or electronics have been running all night on the house side.

Current handling is rated at 140A continuous and 160A for up to 60 seconds, covering the charge and combined accessory demand of most boats, campers and dual-battery vehicles while keeping a clear margin for short peaks.

• Cut-in at 13.3V — the unit links the two batteries once charging voltage is reached, so both banks share the charge current.
• Cut-out at 12.7V with a 5-second delay — the contacts separate only after the delay has elapsed, filtering out brief dips caused by loads or a restart.
• Start battery held in reserve — house loads draw from the auxiliary bank, so cranking capacity is protected at rest.
• Hands-off operation — nothing to switch during launch, mooring or departure preparation.
• 140A continuous / 160A for 60 seconds — sized for typical alternator charge current plus accessory draw.

Plan the cable route first — the unit sits between the two positive feeds and picks up a common ground:

• Mount on a rigid, dry surface close to both batteries, clear of exhaust heat and moving belts.
• Terminate the start battery positive on the main stud and the auxiliary positive on the second stud.
• Ground the unit to a clean chassis or engine-block point and check each lug for a firm seat.
• Match cable gauge to the 140A continuous figure, and fuse long runs at the battery end.
• After start-up, confirm the relay closes once charging voltage passes 13.3V and opens when it settles near 12.7V.

• Boats — splitting charge between start and house banks on outboards, inboards and compact yachts.
• RVs and campers — keeping the leisure battery charged while isolating the vehicle battery from house loads.
• Cars and 4x4s — dual-battery set-ups for fridges, compressors, work lights and recovery equipment.
• Industrial and plant — auxiliary power on trailers, compressors and mobile equipment.

• Minimum order — 1 piece, so samples and trial batches both work.
• Price — negotiable, quoted against quantity and packing requirements.
• Capacity — 500 pieces per week.
• Lead time — 5 to 7 days for standard orders.
• Payment — T/T or Western Union.
• Packing — carton, reinforced for long-haul export shipments.
• Support — selection advice, batch inspection before dispatch, and follow-up on field feedback.