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KeyLine Chargers
KeyLine Chargers Dual Battery Isolator 300 AMP VSR

KeyLine Chargers Dual Battery Isolator 300 AMP VSR

Best price now

$179.87at KeyLine ChargersObserved Nov 3, 2026, 7:44 AM

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Our take on the KeyLine Chargers Dual Battery Isolator 300 AMP VSR

A 300-amp voltage-sensing relay that automatically links a second battery to the charging system once the main battery reaches 13.3 volts, then disconnects when it drops. It ships with a 20-foot 1 AWG red cable, copper crimp lugs and marine ring terminals, and is IP65 rated for engine bays and wet installs. It suits dual-battery setups in trucks, boats and campers running lead-acid, AGM or lithium/LiFePO4 banks. The best new price is $179.87 at KeyLine Chargers as of November 3, 2026, the only new listing found.

Best forDual-battery trucks and overland rigsBoat and marine house-battery installsCamper and van electrical buildsOwners adding a lithium or LiFePO4 auxiliary bank
Pros
  • 300-amp rating handles heavy charging and load currents
  • 13.3-volt cut-in is a sensible threshold for most alternators
  • IP65 sealed against dust and water spray
  • Includes 20 feet of 1 AWG cable with copper crimp lugs
  • Marine ring terminals and screw mounting suit engine-bay installs
Cons
  • Single new listing at $179.87, so no price competition
  • 20-foot cable may be far longer than many installs need
  • Cut-in voltage is fixed, not adjustable
  • No Bluetooth or app monitoring of relay state

KeyLine Chargers Dual Battery Isolator 300 AMP VSR prices at every store

  • KeyLine ChargersNew

    In stock

    $179.87Observed Nov 3, 2026, 7:44 AM
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KeyLine Chargers Dual Battery Isolator 300 AMP VSR price history

Lowest price we've seen: $179.87 on Nov 3 at KeyLine Chargers. Tracked across 1 store since Nov 3.

Specifications

Battery Type
Lithium, LiFePO4
Cable Gauge
1 AWG
Cable Length
20' (6 meter) (red cable)
Connector Type
Ring
Material
Copper (crimp lugs)
Amperage
300 AMP
Voltage
13.3 volts (Cut-in)
Polarity
Positive (battery terminals), Negative (battery terminals)
Battery Terminal Type
Marine
Construction Durability
Heavy Duty
Mounting Type
Screws
Style
Heavy Duty

Questions and answers

Is a 300-amp isolator overkill for a small auxiliary battery?
For a single small aux battery on a modest alternator, yes. A 300-amp rating matters when you run a large bank, a winch or high-current loads through the relay. It works fine on smaller systems but you pay for headroom you may not use.
Does it work with lithium (LiFePO4) batteries?
The listing covers lithium and LiFePO4 as well as lead-acid types. Check that your lithium battery's charging profile and BMS accept alternator charging directly before wiring it in.
What does the 13.3-volt cut-in mean in practice?
The relay closes and connects the second battery once the main battery sees 13.3 volts, which happens when the engine is running and the alternator is charging. It opens again when voltage falls, so the starting battery is not drained by accessories.
Is the 20-foot cable long enough for a truck or boat?
Twenty feet of 1 AWG covers most cab-to-bed or engine-to-stern runs. Measure your route first; 1 AWG is thick and stiff, so tight bends and long runs need planning.
Is it worth $179.87?
That is the only new price found as of November 3, 2026, so there is no cheaper new listing to compare against. The price includes the 20-foot 1 AWG cable and lugs, which offsets some of the cost if you would otherwise buy cable separately.
What is in the box?
The isolator, a 20-foot 1 AWG red cable, copper crimp lugs and marine ring terminals. Mounting screws are used for installation; confirm they are included with the seller before ordering.
Where is the KeyLine Chargers Dual Battery Isolator 300 AMP VSR cheapest?
At KeyLine Chargers, for $179.87, as of our latest check.