How is this different from a plain battery isolator?

A plain isolator switches at one fixed voltage. This one lets you set both the start and stop thresholds and add a 3-60 second delay, so it adapts to lithium or lead-acid and ignores short voltage dips.

Will it charge a lithium auxiliary battery from a lead-acid start battery?

Yes. You set the thresholds to match the lithium bank's needs, and the relay connects the two when the main battery is charging. It passes current; it does not convert voltage.

Do I need a DC-DC charger instead?

If your alternator voltage is lower than your auxiliary battery needs, or you want a controlled charge profile, a DC-DC charger is the better tool. This relay simply links the batteries when the main is up.

What does the delay setting do?

It holds the relay state for 3 to 60 seconds before switching, which stops it cycling on and off when current or voltage fluctuates.

The isolator unit itself. Wiring, fuses and mounting hardware are not included, so plan the cable gauge and fusing for your 140A load.

Can I switch it manually?

Yes. It runs in automatic mode or manual mode, so you can force the link or isolate the auxiliary battery yourself.

Where is the KFFKFF Dual Battery Isolator, 12V 140 Amp cheapest?

At Walmart, for $26.99, as of our latest check.

KFFKFF Dual Battery Isolator, 12V 140 Amp

Best price now

$26.99at WalmartChecked Nov 10

Prices are checked against each store and labelled with when.

Visit Walmart

KFFKFF Dual Battery Isolator, 12V 140 Amp

Best price now

$26.99at WalmartChecked Nov 10

Prices are checked against each store and labelled with when.

Visit Walmart

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Price facts

Last seen at $26.99 at Walmart on Nov 10.

Our take on the KFFKFF Dual Battery Isolator, 12V 140 Amp

The KFFKFF VSR003 is a voltage-sensitive relay that links a main and an auxiliary 12V battery, charging the auxiliary when the main is up and isolating it when the main drops. It handles up to 140A, works with lithium and lead-acid batteries, and lets you set start and stop voltages plus a 3-60 second delay to stop chatter from fluctuating current. A real-time voltage display and manual or automatic modes set it apart from fixed-threshold isolators. It suits dual-battery setups in 4x4s, campers and boats where you want the house battery charged without draining the starter battery.

Best forDual-battery 4x4 and overland buildsCamper and van house-battery chargingBoats with a separate starting and accessory batteryOwners mixing lithium and lead-acid banks

Pros

Adjustable start and stop voltages suit lithium and lead-acid
140A rating covers most auxiliary charging loads
3-60 second delay prevents relay chatter
Real-time voltage display shows both battery states
Manual and automatic modes
Sealed plastic case resists dust and splashes

Cons

Wiring and voltage setup take care to get right
Not a DC-DC charger, so it won't boost a low charge voltage
Plastic housing rather than metal
Voltage thresholds need resetting when you change battery type

KFFKFF Dual Battery Isolator, 12V 140 Amp prices at every store

WalmartNew
In stock
$26.99Checked Nov 10
Visit Walmart

About the KFFKFF Dual Battery Isolator, 12V 140 Amp

This is a 12V, 140A dual battery isolator for vehicles and boats with two batteries. It lets both batteries charge at the same time while keeping power steady to connected devices. It works with lithium and lead-acid batteries and adjusts its charging voltage to the battery type connected.

Start and stop voltages are adjustable. A delay function reduces frequent switching caused by fluctuating current and protects against damage from repeated on-off cycles. A dual voltage display shows battery conditions in real time.

It runs in automatic or manual mode. In manual mode, a fully charged auxiliary battery can reverse charge a drained starter battery, so the engine can be started without jumper cables. The plastic casing resists impact and is designed to keep out water and dust. The unit is compact and can be mounted under the hood or in an off-road vehicle, RV or boat.

Model: VSR003
Rated voltage: DC 12V
Rated current: 140A
Operating modes: Manual and automatic
Delay time: 3-60 seconds
Voltage display: 4.5V-20V
Battery types: Lithium, lead-acid and other battery types
Material: PA6
Color: Black
Dimensions: 3.1 x 2.8 x 2.4 in (80 x 70 x 60 mm), L x W x H
Weight: 0.5 lbs (0.24 kg), including all accessories
In the box: 1 x dual battery isolator kit, 1 x user manual

Specifications

color: MulticolorSource
size: 3.1" x 2.8" x 2.4"Source
Rated Voltage: DC 12VSource
Rated Current: 140ASource

Questions and answers

How is this different from a plain battery isolator?: A plain isolator switches at one fixed voltage. This one lets you set both the start and stop thresholds and add a 3-60 second delay, so it adapts to lithium or lead-acid and ignores short voltage dips.
Will it charge a lithium auxiliary battery from a lead-acid start battery?: Yes. You set the thresholds to match the lithium bank's needs, and the relay connects the two when the main battery is charging. It passes current; it does not convert voltage.
Do I need a DC-DC charger instead?: If your alternator voltage is lower than your auxiliary battery needs, or you want a controlled charge profile, a DC-DC charger is the better tool. This relay simply links the batteries when the main is up.
What does the delay setting do?: It holds the relay state for 3 to 60 seconds before switching, which stops it cycling on and off when current or voltage fluctuates.
What is in the box?: The isolator unit itself. Wiring, fuses and mounting hardware are not included, so plan the cable gauge and fusing for your 140A load.
Can I switch it manually?: Yes. It runs in automatic mode or manual mode, so you can force the link or isolate the auxiliary battery yourself.
Where is the KFFKFF Dual Battery Isolator, 12V 140 Amp cheapest?: At Walmart, for $26.99, as of our latest check.