What a failing battery feels like
As a battery wears out, it loses capacity: the amount of energy it can store and the current it can deliver. At first you might only notice the engine turning over a little slower. Over weeks or months the symptoms build until one morning, usually a cold one, it can't start the car at all.
Some symptoms can come from other parts, like the alternator or starter, which is why a test is the only way to be sure. But if you notice two or more of these, get the battery checked soon.
+ 01 Safety
Signs that need attention right away
A swollen or bulging battery case, liquid on or around the battery, or a rotten-egg (sulfur) smell mean the battery is damaged or overcharging. Don't jump it or try to charge it. Leave it alone and have it replaced, and have the charging system checked too, since overcharging can be the cause.
The eight warning signs
- Slow crank
- The engine turns over more slowly than it used to, worst when it's cold.
- Clicking
- A click or rapid clicking when you turn the key or press start.
- Dim lights
- Headlights and dash lights dim at start-up or at idle.
- Warning light
- A battery or charging light, or a low-voltage message.
- Electrical glitches
- Radio resets, power windows slow, screens reboot.
- Start-stop quits
- On start-stop cars, the system stops shutting the engine off.
- Corrosion
- White or blue-green crust building up on the terminals.
- Age
- More than three years old, or two in a hot climate.
Questions about signs of a bad car battery
Can a battery fail with no warning?
Occasionally, especially from an internal short or a broken connection inside. Most of the time, though, there are signs if you know what to look for.
Is a slow crank always the battery?
Usually, but not always. Corroded cables, a weak starter or very thick oil in the cold can also cause it. A test sorts it out.
What should I do if I notice these signs?
Get the battery tested soon. If it's weak, replacing it before it fails saves you a jump, a tow or a missed appointment.