If You Bought a Used Car, Get a Battery Test ASAP

Americans are forecasted to buy millions of used cars in 2025, despite rising used car prices and market uncertainty. Americans bought 2.88 million used cars in the first three months of 2025, according to reports from industry analysts at Cox Automotive. That retail sales volume beats their 2025 forecasts, which were revised to between 37.6 million and 38 million used cars sold in the year ahead.

If you’re buying a used car in 2025, there’s one car part you should probably replace on your new vehicle as soon as you get the key: The car battery.

That said, the used car might be in great shape even if the battery isn’t. Most mechanics inspecting a used car before purchase may skip the car battery because it’s not a deal breaker. They’re looking for critical reasons not to buy the car, such as knocking noises in the engine or burnt-smelling transmission fluid. Now, a technician may recommend replacing the battery if they see it’s older than four years. (Most car batteries last 3-5 years.) The truth is, you may need to replace it much sooner.

If you just bought a used car, get a battery test at a reliable repair shop or favorite battery store.

Weak batteries may even be expected when you buy a used car. Here’s why.

Used cars may sit idle for several days, which can hurt the car battery.

As we’ve explained elsewhere, car batteries need the occasional drive. Used cars, on the other hand, are more valuable with low mileage. Of course, most dealerships won’t drive their fleet around to keep the battery from getting weak by sitting unused.

Instead, that’s what reconditioning repairs are for. Recon fixes improve a vehicle’s condition, including fixing dents, windshield cracks, oil changes and more. (They may replace the battery if the car won’t start. We’ll talk about that next.)

After the restorating, a used car may sit for days or weeks waiting for its next owner. Occasional, 15-minute test drives might be the only time the alternator gets to work — and those short drives aren’t enough to give the battery a healthy charge.

Used cars may have refurbished batteries, which may not last in the long run.

During reconditioning, the tech may have found the battery was mostly dead already — and replaced it with a refurbished battery.

Refurbished batteries are car batteries on an extra life. They may have failed or have significant wear and tear — and still be able to conduct electricity. High-quality refurbished batteries can pass conductance tests, not just voltmeter tests. That said, they’re not ideal in the long run because they may not withstand much more wear and tear.

They’re ideal for car dealerships to keep your car’s purchase price lower. However, the used car may have sat idle for weeks. That’s hard on any battery. Add that idle time to an already-worn battery and you’ve got a risky battery situation.

To make matters worse, that worn battery may have sat idle for weeks in the heat.

Used cars may sit parked in the heat all day, which also hurts the car battery.

Temperatures hotter than 90 F can wear down car batteries, even if they're just sitting in a used car lot.

Heat is a slow problem. It’s different from how a battery can suddenly die in winter. Heat steadily weakens batteries by causing water to evaporate from the electrolyte inside. That leaves a more-acidic mixture right beside the sensitive components. Corrosion that might have taken years can happen in several extremely hot days.

Runaway corrosion on the battery reduces how much charge a car battery can hold. It’s like a wornout phone battery that only lasts five minutes after hours of recharging. Pretty soon, the car battery can’t hold enough power to start the engine, even if it’s been recharged well.

Heat leaves lasting damage hidden on car batteries.

Even if your used car starts now, there’s no guarantee it can handle a slight temperature drop in a few months.

That’s why it’s so important to get a battery test as soon as you get the title and registration for your used car.

Does a bad battery mean I got a bad deal on my used car?

Not at all. Sitting unused for days, in the heat, with a used battery — that’s hard on any car or truck. Used cars are just more vulnerable to battery issues because they’re between owners.

The techs who restored your used car or truck were focused on more critical issues to make sure the vehicle runs. Car batteries, while they’re critical to every drive, are designed to be replaced. Most batteries last three to five years, and if your used car is 12 years old, it might be time for a new battery.

Now that the car is yours, you can treat it well with a premium, long-lasting battery.