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How to Keep a Car Battery Alive in Winter Storage

By Garage Trials Updated 3 min read Lesson 2 of 2

2 lessons in this series, 5 min in total
  1. Will a Car Battery Die Sitting All Winter? 2 min read
  2. How to Keep a Car Battery Alive in Winter Storage 3 min read

This lesson draws on NOCO’s GENIUS1 user guide, the Battery Tender Junior manual, Consumer Reports, Yuasa and Battery University, each credited where it appears. See how we research.

Maintainer, trickle charger or disconnect?

A smart maintainer charges the battery, then drops to a float or maintenance mode and tops it up only when needed. Consumer Reports recommends one for stored cars, to keep the battery topped off without overcharging it. Both the NOCO GENIUS1 guide and the Battery Tender Junior manual say the charger can stay connected indefinitely once the battery is full.

An older trickle charger may lack that mode, so check the manual before leaving any charger on for months. The difference is covered in battery charger vs maintainer.

Consumer Reports suggests disconnecting the negative (black) cable if you can’t drive the car for at least 20 minutes about every two weeks. That stops the car’s systems from drawing power, but self-discharge continues, so the battery still needs voltmeter checks. Consumer Reports also warns that the radio and navigation system may lose their memory and may ask for a security code.

Option Stops electronics drain Stops self-discharge Catch
Smart maintainer Tops up the loss Tops up the loss Needs an outlet nearby
Unregulated trickle charger Tops up the loss Tops up the loss Can overcharge, no float mode
Disconnect negative cable Yes No Voltmeter checks
Battery out, on a maintainer indoors Yes Tops up the loss Needs a warmer, ventilated spot

Hooking up for storage

With the battery still in the car, the clamp order is the same as for any charge, and can you charge a car battery without disconnecting it walks through it.

For a battery outside the vehicle, both manuals add a step. Attach an insulated 6-gauge cable at least 24 inches (61 cm) long to the negative post. Connect the red clamp to positive, then stand back and connect the black clamp to the free end of that cable.

Both chargers can also connect with ring (eyelet) terminals, per NOCO’s guide and the Junior manual, and these can stay bolted to the battery all season. Both manuals say to charge in a well-ventilated area, never set the battery on the charger, and never charge a frozen battery. A flat battery left in the cold is the one at risk; see why a flat battery freezes.

Special cases: battery out, motorcycle, boat, lithium

Battery out. Yuasa’s two rules are to keep the battery out of freezing cold and keep it charged. If the car sits somewhere cold with no outlet, removing the battery and keeping it on a maintainer in a warmer, well-ventilated spot covers both.

Motorcycles. Yuasa says a bike’s fuel-injection computer, clock and radio can drain the battery even with the ignition off. It recommends checking a stored conventional (flooded) battery every month and an AGM battery about every three months, and more often below 60°F (16°C) or above 80°F (27°C).

Boats. Both manuals say a marine battery must be removed and charged on shore, because charging on board takes equipment designed for marine use.

Lithium in an unheated garage. Battery University says consumer-grade lithium-ion batteries can’t be charged below 32°F (0°C), because a sub-freezing charge plates metallic lithium onto the anode. NOCO’s guide says the GENIUS1 pauses when the air is colder than -4°F (-20°C) and resumes once it warms up. Check the battery maker’s limits before charging lithium in an unheated garage.

To match a maintainer to your battery, see which maintainer fits an AGM, lithium or 6V battery.

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