Why Southern California Heat Kills Car Batteries

Ask most people what kills car batteries and they'll say cold weather. In Pasadena, it's the heat. Batteries here often give up after three or four years, and many fail in the middle of a summer heat wave or right after one. Here's why, and what to do about it.

Why heat is worse than cold

A car battery stores energy in a chemical reaction. Heat speeds up that chemistry, including the reactions that slowly destroy the battery from the inside: corrosion of the internal plates and evaporation of the electrolyte. Under the hood on a 100-degree day, temperatures get far higher than the air outside. Every summer takes a bite out of the battery's life. Cold weather just reveals the damage, because a weakened battery has less in reserve on a chilly morning.

Warning signs

• The engine cranks slowly when you start it
• Headlights dim at idle and brighten when you rev the engine
• The battery or charging warning light comes on
• You've needed a jump start recently
• White or blue corrosion on the terminals
• A swollen or bulging battery case, a sign of heat damage
• The battery is more than three years old

Is it the battery, or something else?

A dead battery isn't always a bad battery. A failing alternator won't recharge it as you drive. A loose or corroded cable can block power to the starter. A parasitic drain, like a module that won't go to sleep, can empty a good battery overnight. That's why testing matters. We test the battery, the alternator output and the starter, and track down drains as part of our electrical repair work.

The smog-check gotcha

Here's something most people don't know: replacing or disconnecting your battery resets the car's emissions readiness monitors. If you go straight to a smog check afterward, the car can be rejected as "not ready." After any battery work, drive normally for several days, a mix of city and freeway, before your smog test. Read more in our post on check engine lights and smog.

How to make a battery last longer

• Park in the shade or a garage when you can during summer.
• Keep terminals clean and tight. Corrosion acts like resistance in the circuit.
• Test it every year after year three. A load test takes minutes and can be done during an oil change.
• Make sure it's held down. Vibration shortens battery life.
• Drive long enough to recharge. Lots of very short trips with the A/C on can drain it over time.

Replacing it the right way

A replacement should match your vehicle's size, terminal layout and cold cranking amp rating. Many newer vehicles with start-stop systems need AGM batteries, and some need the new battery registered with the computer. See our battery service page.

Get tested in Pasadena

Stop by Walnut Smog & Repair at 1323 E Walnut St #2 before summer, or as soon as you notice slow cranking. Call (626) 449-6252.

Book a visit at Walnut Smog