Both, in different ways. Summer does the damage; winter reveals it.
Heat shortens battery life
AAA names time, heat and vibration as the three factors that decide how long a battery lasts. Its guidance is roughly three to five years: about three in hot southern climates, and five or more in cooler northern ones. Heat speeds up the chemical reaction inside the battery, and it speeds up the wear too. A battery that lives through several hot summers is losing capacity every year, even if it still starts the car.
Cold is when a weak battery gives up
A cold engine is harder to turn over and a cold battery delivers less. A battery that coped in August with plenty to spare may not have enough left on the first freezing morning. That is why failures bunch up in winter, even though the ageing happened earlier.
What to do before each season
Before summer
- Make sure the battery is held down firmly so vibration does not wear it.
- Keep the terminals clean and tight.
- In a hot climate, treat three years as the point to start testing, not to start worrying.
Before winter
- Test the battery once it is past year three. Our voltage checker turns a multimeter reading into a plain verdict.
- If it is weak, replace it on your terms rather than on a freezing morning. Compare prices in the calculator.
- Read cold weather battery care.
How old is yours?
The battery life estimator compares your battery’s age with the typical life for your climate and gives a replace-now, plan-soon or likely-fine result. It is an age-based estimate, not a test, so confirm with a voltage reading.
For the full picture, see how long do car batteries last?.