1) Clicking sound when you turn the keyThe first and probably most obvious sign of a failing battery is a clicking sound when you turn the key. When your key turns in the ignition, your car battery is supposed to send an electrical signal to the starter—that's what gets your engine going. If your battery is weak or failing, it will struggle to make this connection; in turn, the starter receiving reduced or insufficient power from the battery will often make a clicking noise. Often, there will be a few "warnings" before your battery won't start at all. You should bring your car in for service at the first sign of trouble with your starter. Don't wait until the engine can't turn over.
2) Dim headlightsA less obvious sign that your car battery is failing is dimming lights. If your battery is failing it won't be able to power your car's electrical components, like your headlights. If you notice that your headlights seem dim, bring your car in for service as soon as possible. This could be an early warning sign that your battery is almost dead.
3) BackfiringAnother sign your car battery is failing is backfiring. Here's how it works: A failing car battery can sometimes cause intermittent sparks—sparks that cause fuel to accumulate in the engine's cylinders. If built-up fuel is ignited, it will cause your car to backfire. Backfiring can be a symptom of several different problems, so your technician will want to perform a battery test to be sure. Cleaning your batteries can help to prevent this in the fut
Read more in our recent article Car Battery Replacement: When is it time for a new battery?