Car battery Buying Guide from Consumer Reports

Getting started

Throughout the life of your vehicle, you will probably have to replace your car's battery a number of times. Either it gets old and has to be replaced, or it is drained unintentionally when lights or another electrical accessory are left on. A dead battery can be a hassle, especially if you cannot find jumper cables or have to wait for roadside assistance. Being proactive in replacing your battery can ensure that your car is ready to go when you are. Through this battery buying guide, we will advise on considerations for battery ownership and replacement.

Battery maintenance

With a maintenance-free or sealed battery, you don't have to check or refill the electrolyte levels. While most have a flat top, some batteries with caps also are claimed to be maintenance free.

While manufacturers claim that absorbent glass mat (AGM) batteries are safer, they cost more than conventional batteries that perform almost as well or better in our car batteries comparison. It might make sense to consider a top-scoring AGM battery only if your car's design makes the battery difficult to reach.

Make sure the battery fits your car and driving needs

When the time comes to buy a replacement battery, make sure you get the right size and design (or type) for your vehicle. Check your owner's manual or an in-store fit guide before shopping.

Choose a battery that fits your climate and driving conditions. A model that did well in our battery-life testing, for example, is critical if you live in a warmer climate. Frequent high temperatures are very tough on batteries, increase corrosion of plates, and more quickly vaporize the electrolyte that is needed for current. Long life is also important if you make many short trips that don't allow much time for recharging.

Along with good life-testing performance, choose a battery that scored well in our cold-cranking amps and reserve-capacity testing. Most products in our car batteries comparison have proved to be at least adequate in both of those tests, but there is performance variation.

How to choose the battery

All batteries lose strength over time, even when idle. So choose one no more than six months old. Most have a shipping code on the case. Some use a letter for the month ("A" for January) and a number for the year ("8" for 2008); others use a numeric date.

All things being equal, favor a model with a helpful plastic loop. Such a handle makes it easier to lift and carry batteries, which weigh about 40 pounds, and just as important, aids in lowering the battery onto the tray in tightly packed engine compartments.

Battery recycling

A battery's toxic lead and acid can easily be recycled, and most retailers will dispose of the old one for you. You might pay a charge that's refunded if you bring in the old battery after installing the new one.

Types

Batteries come in a variety of sizes and it's important to choose the right size. The wrong size might not fit securely or provide sufficient power. If the terminals are in the wrong place, your car's cables might not reach, or it may not fit securely. Check your owner's manual or an in-store fit guide.

Size 65 (top terminal)

Fits large cars, trucks and sport-utility vehicles from Ford or Mercury.

Size 75 (side terminal)

Fits some General Motors midsized and compact cars and a few Chrysler vehicles.

Size 24/24F (top terminal)

Fits many Acura, Honda, Infiniti, Lexus, Nissan, and Toyota vehicles.

Size 34/78 (dual terminal)

Fits many large Chrysler vehicles and many 1996-2000 GM pickups, SUVs, and midsized and large sedans.

Size 35 (top terminal)

Fits most Japanese nameplates, including many recent Hondas, most Subarus, and most Nissan and Toyota vehicles.

How we test

Our battery-life test is based on a standard recently adopted by the Society of Automotive Engineers (SAE). Our test includes partially draining and then recharging each battery almost 3,000 times over a 10-week period, during which the battery must meet voltage and amperage limits based on real-life demands. The highest scorers maintained higher voltages and were able to withstand more cycles.

In addition to our endurance tests, our reserve-capacity test measures how long an auto battery can supply power if the charging system fails or if you leave your headlights or accessories on. The lowest-scoring models in our test should provide 1½ hours of power. Higher-scoring models can supply power well past two hours.

We also test for cold-cranking amps. That's the measure of current that's available at 0º F and is the primary indicator of cold-climate performance. CCA has long been a major selling point for batteries. But we believe that the industry's claimed CCA doesn't reflect real-world conditions because batteries are charged at a higher voltage than the 14.5 volts provided by most vehicles' alternators. Our CCA test is based on more realistic charging voltages and amperage demands, and our results show each battery's relative cranking power, regardless of the manufacturer's claims.

Brands

Most aftermarket car batteries sold in the United States are made by three companies that build them for retailers: Johnson Controls, which supplies more than half of the market, Exide, and East Penn. They are sold under various names and built to the specifications of retailers, so performance can vary. Most stores will test, install, and match the right battery to your car’s needs. Here are the major brands and where they are sold:

AutoCraft

Available at a variety of Advance Auto Parts stores across the country.

Bosch

Available at Pep Boys.

DieHard

Available at Sears and Kmart automotive centers.

Duralast

Sold at AutoZone.

EverStart

Available at Walmart stores.

Interstate

Available at a number of auto parts stores, repair shops, and online.

Kirkland Signature

Sold exclusively through the Costco warehouse club. Membership to the store is required before you purchase.

NAPA

Sold through NAPA auto-parts stores.

Nascar Select

Sold through NAPA auto-parts stores.

Warranties

A decade ago, a battery's free-replacement period was as little as three months, and the prorated period (which allows only partial reimbursement) might have been just 50 months. Today, a 36-month free-replacement warranty is typical, and the prorated period can be up to 108 months.

But even with today's longer warranties, it's still important to choose a battery with the longest free-replacement period you can get.

A battery warranty code of 24/84, for example, indicates a free-replacement period of 24 months and a prorated warranty of 84 months. But the amount you'll be reimbursed usually drops off pretty quickly once you're into the prorated period.

For example, the Duralast Gold 34DT-DLG carries a 96-month prorated battery warranty. Using the formula listed on the manufacturer's Web site, this means that after four years, or half the warranty period, you would be credited with half of the original price if the battery failed.

Signs of neglect, such as low-water levels and improper installation, can void a warranty. So can use in heavy-duty applications such as high-end car audio and marine use if the battery is not recommended for them.