What is a dual battery isolator relay used for?

It connects and disconnects a second battery from the main one. With the engine running, both charge; with it off, the auxiliary loads run off the second battery and the starting battery stays charged.

Does it come with a wiring harness?

No. The package contains the relay only. You supply the cables, terminals and any switch or trigger wiring.

Is 500A enough for a winch or starter?

The relay is rated 500A at 12V DC, which covers most winches and heavy accessory loads. Check your load's surge current and use short, thick cables.

Can it be mounted under the hood?

The phenolic housing is water resistant, so it suits engine-bay mounting. Keep it away from direct spray and standing water.

The two large studs carry the battery cables and the small pins take the on/off control signal. Confirm the pin layout on your unit before wiring.

Unbranded

Dual Battery Isolator Relay Start On/ 4 Pin 500A 12V

Best price now

$19.09at WalmartChecked Nov 10

Prices are checked against each store and labelled with when.

Visit Walmart

Unbranded

Dual Battery Isolator Relay Start On/ 4 Pin 500A 12V

Best price now

$19.09at WalmartChecked Nov 10

Prices are checked against each store and labelled with when.

Visit Walmart

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Price facts

Last seen at $19.09 at Walmart on Nov 10.

Our take on the Dual Battery Isolator Relay Start On/ 4 Pin 500A 12V

This is a 4-pin, 500-amp continuous-duty relay for 12V dual-battery setups. It isolates the auxiliary battery so the starting battery does not drain when accessories run with the engine off. The black phenolic housing is water resistant, and the compact body fits tight engine bays. It is a generic part, so expect no wiring harness or mounting hardware in the box; branded isolators often include those. Buyers of this class of relay value the high current rating and simple on/off operation, but quality varies between unbranded units.

Best forDual-battery 12V vehicle buildsOverland and camper electrical setupsMarine and RV auxiliary battery banksDIY wiring projects needing a high-current switch

Pros

500A rating at 12V DC handles heavy loads
4-pin on/off design is simple to wire
Water-resistant phenolic housing
Compact size fits crowded engine bays
Helps prevent the starting battery from draining

Cons

No wiring harness, terminals or mounting hardware included
Unbranded unit, so build quality is inconsistent
No diode or smart charging control
Water resistance is splash-level, not sealed for submersion

Dual Battery Isolator Relay Start On/ 4 Pin 500A 12V prices at every store

WalmartNew
In stockSold by Mrain SkyReturns: Sold by a Walmart Marketplace seller; returns go to the seller under the seller's returns policy.
$19.09Free shippingChecked Nov 10
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About the Dual Battery Isolator Relay Start On/ 4 Pin 500A 12V

This is a 12V dual battery isolator relay with 4 pins and an ON/OFF type switch. It is rated for a maximum of 500 amps at 12V DC. It keeps the primary battery from discharging and extends battery life.

The housing is water resistant black phenolic plastic. The relay suits universal 12V applications.

Type: Dual battery isolator relay (ON/OFF)
Voltage: 12V DC
Max rating: 500 amps at 12V DC
Pins: 4
Material: Water resistant black phenolic plastic
Color: Black
Dimensions: 7.2 x 5.5 x 8.5 cm (2.8 x 2.2 x 3.3 in), L x W x H
In the box: 1 x 500A 12V relay

Specifications

color: BlackSource
size: 7.2cm x 5.5cm x 8.5cmSource

Questions and answers

What is a dual battery isolator relay used for?: It connects and disconnects a second battery from the main one. With the engine running, both charge; with it off, the auxiliary loads run off the second battery and the starting battery stays charged.
Does it come with a wiring harness?: No. The package contains the relay only. You supply the cables, terminals and any switch or trigger wiring.
Is 500A enough for a winch or starter?: The relay is rated 500A at 12V DC, which covers most winches and heavy accessory loads. Check your load's surge current and use short, thick cables.
Can it be mounted under the hood?: The phenolic housing is water resistant, so it suits engine-bay mounting. Keep it away from direct spray and standing water.
How is it wired?: The two large studs carry the battery cables and the small pins take the on/off control signal. Confirm the pin layout on your unit before wiring.
Where is the Dual Battery Isolator Relay Start On/ 4 Pin 500A 12V cheapest?: At Walmart, for $19.09, as of our latest check.