How hot weather affects your car battery

How hot weather affects your car battery

Consumer Reports tests 150 batteries in total each year in their lab (including five examples of each rated model), charging and discharging them thousands of times to see how long they will last. If you live in a hot area or have particular concerns about summer performance, pay special attention to the degree of battery life in our ratings.

Battery life is measured by repeatedly discharging and recharging at a test temperature above 167 degrees Fahrenheit for 15 weeks or until performance drops to unacceptable levels. This simulates the summer temperatures that the battery could experience in the engine compartment. (Learn more about how we test car batteries.)

Car batteries come in many sizes. Among the ones we tested, there is great variance in determining the best performers from year to year, and from volume to volume. This makes it impossible to make simple recommendations by brand or model. This also means that you should not assume that buying the same battery model you are replacing will get the same results.

One trend is clear: Many of the top grades are pricey Absorbent Glass (AGM) batteries, known for their long service life and ability to withstand deep discharge — when the battery is heavily discharged to 10.5 volts or less, such as when the lights are left on overnight.

“If you live in an area with high temperatures, and are looking for a maintenance-free battery, consider getting an AGM,” says CR’s Gallottaveori. “Although AGM batteries can also be affected by high heat, they tend to perform better overall than the other sealed batteries in our tests.”

he He adds, “We’ve seen that most AGM batteries excel in heat-focused lifetime testing, based on 15 weeks of continuous testing at over 160 degrees.”

But even AGM batteries face challenges. “AGM batteries will perform well in the heat, but the life span will be hampered by … high temperatures,” says Jeff Barron, director of the Interstate Battery Research Laboratory.

Barron explained that while some conventional batteries, known as “flooded,” can regenerate water (with distilled water) to extend their operational life, AGM batteries are sealed.

In addition to routine inspections, Barron advises car owners to keep their batteries fully charged and to avoid leaving their car parked unused for long periods of time. This is especially true for AGMs. If you must store a car for weeks or longer, a battery tender can help ensure that the battery will be ready to start the car when needed. Make sure the bid is suitable for your car battery.

Some flooded batteries are offered in northern and southern versions, each designed for specific challenges of different climates. Northern batteries emphasize the cold cranking amplifier (a measure of how well a battery runs an engine during extreme cold weather), while Southern batteries have higher electrolyte-to-lead ratios that enhance durability in the heat.

Most stores carry the appropriate battery for your area. The general battery, without a regional focus in its design, could perform well in the temperate zone lying between the extremes, such as the mid-Atlantic states.

Barron says that in some cases, owners can replace the AGM battery with a sunken battery to increase longevity in hot climates, but it’s best to consult a mechanic first. Many vehicles now come with AGMs to support an increasing array of electrical components, and the charging system may be configured specifically for the AGM’s charging needs.

Cars and their batteries are becoming more capable and sophisticated. This can add complexity to the once simple battery replacement task.

Barron points out that some recent models from Audi, BMW, Ford, Mercedes-Benz, and others require the battery to be registered by the vehicle, so it can optimize charging and usability. This usually requires a mechanics scan tool, a professional device that interfaces with the car’s computer system. Even older vehicles can require some level of reprogramming by a mechanic when changing the battery to allow all systems to operate. Ultimately, this means that many DIYers may find that they need help from a professional.

“For best long-term performance when replacing the battery, check CR ratings, consult your owner’s manual, and consult a technician,” Gallottaveori says.

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