How To Test Your Battery BEFORE It Fails This Winter

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Chances are good that if you end up having to call AAA, it’s going to be because of a dead battery. In 2014, AAA responded to 29 million calls. 17 million of those calls were due to a dead battery. Most of those calls could’ve been avoided by testing the battery ahead of time. Here’s how to do it.

There’s nothing worse than the impotent “click-click-click” of a battery that’s strong enough to turn on the lights, but too weak to spin the starter.

Depending on your driving habits and the weather, your battery can fail at an alarmingly rapid rate, especially in a modern car. Even the most basic of 2016 models has power-hungry accessories that are always on, no matter whether the car is running or not. Security systems, keyless entry and remote start all require functions that remain on at all times, whether the car is running or not.

Short trips that don’t allow the battery to fully charge, or any kind of moderate-term storage can deplete a battery. Throw in one cold morning and your commute just got a lot longer.

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Acid Stratification

If your battery sits at below an 80 percent state of charge, never receives a full charge and charges and discharges quickly (as in a short trip), the battery may suffer from a condition called acid stratification. The problem is particularly an issue on modern luxury cars with a lot of parasitic draw and many power-sapping accessories.

In a normal battery, the electrolyte is distributed equally throughout the battery case (top image).


In a stratified battery, the electrolyte settles toward the bottom of the battery (bottom image), leaving more water at the top. The light concentration of acid at the top causes corrosion of the lead plates inside, and limits plate activation, reducing the Cold Cranking Amps (CCA) the battery can produce. Because there’s a high concentration of acid at the bottom of the battery, it can cause the battery to read as if it has a full or nearly full state of charge. Severe acid stratification can cause sulfation of the plates, effectively destroying the battery’s ability to hold a charge.

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Low Charge

During cold months, batteries dwell at just 75 percent charge level. Making short trips, or spending most of your commute in gridlocked traffic doesn’t help. Add in the fact that you’re probably idling with the headlights, radio, heat, heated seats, rear window defroster and wipers, and the alternator never has a chance to fully replenish the battery. Day after day, week after week, the situation gets slightly worse until that one frigid morning when the car won’t start at all.

But there are ways to both test the battery ahead of time, and help the battery and charging system cope with the falling temperatures. And unless you want to purchase the equipment, you can actually have the battery tested in minutes for free.

Battery Testing

You can use a multimeter to test the battery’s current state of charge, but all it tells you is at that moment, without a load, the battery is hovering around 12 volts. The green “eye” on the battery tells you that much.

What you need is a tester that not only tests the current state of charge at rest, but also the battery’s ability to maintain its voltage during a start cycle. That’s where a load tester is invaluable.

Battery Load TesterSimple load testers like this one are good to have around the garage. They don’t require batteries, so they’ll work every time you take them out of your toolbox. The red and black leads connect to the battery terminals. The Load Switch simulates a start cycle. Flip the switch for 10 seconds, and the battery is stressed the way it would be when you turn the key. The easy-to-read gauge face tells you when it’s time to replace the battery.

This video shows how to read a load tester:

A tester like this one not only tests the battery during a load, but at rest, as well. And with the engine running, it also works as an ammeter, showing whether or not your alternator is putting out the 13.4 volts it’s supposed to.

Load testers are available everywhere automotive tools are sold, and generally run in the $50 range.

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The Free Solution

So you don’t want to spend $50 for a tool that you’ll use once a year? There’s a free solution, too.

Most auto parts stores have more sophisticated versions of these simple load testers. They’re in the business of selling batteries, so it’s to their advantage to warn you when yours is reaching a point where it’s no longer able to hold a charge.

Auto parts retailers like AutoZone will test a battery that allows the clerk to enter much more specific information to get a more accurate reading. The tester requires the battery’s CCA (Cold Cranking Amp) rating, the ambient temperature, and several other variables. The tester then runs a similar load test to measure the battery’s ability to start your car.

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Preventing a Dead Battery

If your battery is healthy enough to accept a charge and your charging system is working properly, your car should start every time. However, if you’re leaving the car parked for an extended period, say more than a week, then you may consider trickle charging it to ensure the battery dwells at more than 80 percent of its full charge.


Ordinary trickle chargers work, but they need to be monitored. A microprocessor-controlled automatic battery charger like the Battery Tender doesn’t. Simply plug it in and it monitors the state of charge constantly, applying a charge only when the battery needs it.

Single application Battery Tenders retail in the $50 range. If you have two cars, a motor scooter and a snowblower with an electric start, then you might consider the $189, four-bank Battery Tender that can trickle charge all four items simultaneously.

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Craig Fitzgerald

Craig Fitzgerald

Writer, editor, lousy guitar player, dad. Content Marketing and Publication Manager at