How Heat Affects Car Batteries and How to Protect Yours
Many people think cold weather is the enemy of car batteries. Cold makes an old battery hard to start, but heat is what actually wears it out. In a hot country, a battery that would last four or five years elsewhere may only last two or three.
Short version: high temperatures speed up the chemical reactions inside a battery and cause it to lose water and corrode. Park in the shade, keep the terminals clean and check your battery every few months.
What heat does inside a battery
- Faster chemical wear. Higher temperature speeds up the reactions that slowly damage the lead plates.
- Water loss. In batteries that are not fully sealed, the liquid inside evaporates faster, exposing the plates.
- Corrosion. The internal grids and the terminals corrode more quickly.
- Sulfation. A hard crystal layer can build up on the plates, especially if the battery stays partly discharged. This reduces its ability to hold charge.
The damage builds up over months. The failure often shows up later, when the weather turns cooler or after a long time parked, because a weakened battery has less reserve.
Under the bonnet is hot
Even when the outside air is warm, the engine bay can be much hotter. Batteries with a heat shield or cover fitted by the maker should keep it on. If your car has a plastic cover or insulating sleeve, do not remove it.
Ways to protect your battery
- Park in the shade or in a garage when you can.
- Keep terminals clean. Remove white or blue-green crust with a mixture of baking soda and water and a small brush. Dry, reconnect and tighten.
- Check the hold-down. A battery that shakes around wears faster.
- Check the water level if your battery has removable caps. If the plates are exposed, top up with distilled water only, never tap water or acid. Fill to the level marked and do not overfill.
- Take longer drives. Repeated short trips do not give the alternator time to recharge the battery after starting.
- Turn off accessories such as lights, radio and phone chargers before switching off the engine, and avoid using them with the engine off.
- Get it tested once a year after the battery is two years old. Many workshops will do a free voltage check.
Signs that heat has already damaged it
- A swollen or bulging case
- Low fluid level or dry-looking plates
- Heavy corrosion around the posts
- A rotten-egg smell
- Slow cranking even after being fully charged
If you notice any of these, read our guide on the signs your car battery is failing. A swollen or leaking battery should be replaced.
Choosing a battery for hot conditions
When you buy a new one, look for a sealed, maintenance-free model with a fresh manufacture date, and ask whether the maker designs it for hot climates. Our guide to choosing the right car battery lists what to check.