How to Keep Batteries Alive Through Winter

Idle batteries kept in tractors during the winter will probably see their death during those cold months. Get tips on how to maintain batteries while they’re not in use.

By Dave Mowitz Updated on April 2, 2025

Ask collectors about the number one headache involved in keeping tractors running and they will likely snort, “Dead batteries.”

Indeed, few batteries — even premium-quality products— seem to last longer than a couple of years on old tractors. Don’t blame the battery or its maker, although cheaper-quality products do have a tendency to be short-lived.

Battery failure is often caused by long periods of inactivity. Batteries idling in cold weather are particularly vulnerable to failure. Often it’s not the use but the disuse that kills batteries. A battery is like a piggy bank: if you keep taking out and putting nothing back, you will soon have nothing.

Keep Them Charged

The most important chore when storing tractors for the winter is keeping the batteries fully charged. Batteries kept at 75% or less of their charge capacity are vulnerable to sulfation buildup, which occurs when the sulfuric acid molecules in battery fluid attach themselves to the battery’s lead plates. If the battery is immediately recharged — as will happen when an engine is running — the sulfuric acid returns to the electrolyte fluid.

In batteries not kept fully charged, the sulfuric acid tends to stick to the lead plates. After a short time (sometimes less than a month), these plates become so coated they can never be recharged. When storing batteries, avoid placing them on a full charge for the entire winter. This will kill a battery faster than disuse. Instead, utilize a new-generation smart charger that gently maintains condition. They can sense a battery’s charge level and replace energy as needed. If you keep a battery fully charged all the time, sulfation is not a problem.

Testing Batteries

A battery must be fully charged before the test, and the battery’s surface charge must be removed before testing. A battery sitting several hours (12 hours is preferable) after recharging is ready to test. Otherwise, a battery must experience a load of 20 amps for three to five minutes to remove its surface charge. This can be done by turning the headlights on for several minutes.

To test with a hydrometer, draw off an electrolyte solution (water and sulfuric acid) sample from each cell of the battery. Reading the colored floats and comparing them to the guide on the hydrometer, you will be able to determine the specific gravity of the electrolyte. This reading measures the percent of water to sulfuric acid in the battery. New batteries are composed of 64% water and 36% sulfuric acid.

As a battery discharges and recharges repeatedly over time, some of the sulfuric acid attaches itself to the battery’s lead plates in a process called sulfation. Sulfation, the cause of 80% battery failures, also increases the percent of water in the battery, which decreases the specific gravity of the electrolyte solution.

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Store Them for the Winter

So your best bet is to remove the battery from the tractor and keep it charged in storage. By the way, storing batteries on concrete floors does not cause them to discharge any faster than if they are sitting on a wooden shelf. This myth was perpetuated in the early 1900s when battery cases were made of porous material.

Today’s polypropylene or hard rubber-encased batteries are sealed better, so external leakage discharge is no longer a problem.

More Storage Steps

• Test electrolyte levels in each cell. Replace fluid as needed because lead plates exposed to air will coat with sulfate. Avoid overfilling cells, and do not use tap water in batteries because it may contain minerals that can contaminate the fluid.

  
  

• Wash batteries with a mixture of baking soda and water. This solution helps neutralize and wash away any sulfuric acid that spilled out of the battery.

  
  

• Clean battery terminals and coat them with petroleum jelly.

• Store batteries in a warm, dry location. Do not store them in your home or in any location near open flames. Avoid storage locations that are either extremely cold or hot; batteries discharge as temperatures increase. A battery left sitting for 24 hours at 110°F would not be able to start an engine after just 30 days. On the other hand, a discharged battery stored in subzero temperatures can freeze.

  
  

• Maintain a battery’s charge. Batteries, especially over time, lose their charge due to their natural chemical processes. Hook batteries up to a combination battery charger/maintainer or a simple battery maintainer. Battery maintainers are not the same as a trickle charger, which continues to energize even after the battery is fully charged which can result in overcharging. If you use a trickle charger, you must monitor and disconnect the battery at the correct time. A battery maintainer detects and counteracts the loss with a small amount of amperage to top up the battery without overcharging the unit.

Get a Smart Charger

Purchase a charger regulated to maintain a battery at normal levels for long storage periods. Such smart chargers use a microprocessor that senses when a battery has reached its peak charge and then switches to a float mode. This feature maintains voltage at a level sufficient to keep a battery from discharging, but it also prevents it from being overcharged.

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