Is it my battery or my alternator?
If your car starts after a jump and then runs fine but won't restart the next morning, the battery is usually the problem. If it dies while you're driving, the lights dim and flicker, or the battery warning light comes on, suspect the alternator. A battery test and an alternator output test together give a definite answer in minutes.
Quick comparison
| Symptom | Battery | Alternator |
|---|---|---|
| Slow crank or clicking in the morning | Likely | Possible |
| Starts with a jump, runs fine, dies overnight | Likely | Less likely |
| Dies while driving | Unlikely | Likely |
| Battery light on while driving | Unlikely | Likely |
| Headlights dim at idle, brighten when revving | Possible | Likely |
| Whining noise from the engine that rises with RPM | No | Possible |
| Battery is 4 or more years old | Likely | n/a |
The third possibility
If both test fine, there may be a parasitic draw: something staying on after the car is off. We measure the current draw with the car asleep and track it down circuit by circuit.
What we do
A full charging-system check: battery load test, alternator output and ripple, cable and ground connections, and a draw test if needed. One customer arrived with a dead car and left the same day with a new alternator.
From drivers who came to us
My car died yesterday… they were so kind and helped me out by installing an alternator and I was on the road again.
My Lexus CT 200H was in dying need of a new battery after nine years with over 146K miles… They got my car up and running by replacing a new starter battery and rear shocks since they were leaking by the end of the day.
Excerpts from verified customer reviews on Yelp.
More questions
Can a bad alternator ruin a new battery?
Yes. An alternator that undercharges leaves the battery repeatedly drained, which shortens its life. One that overcharges can damage it too.
What voltage should a car battery read?
About 12.6 volts with the engine off and fully charged. With the engine running, the charging system usually holds roughly 13.5 to 14.7 volts.
My battery is new but keeps dying. Why?
Something may be drawing power with the car off (a parasitic draw), such as a module that won't sleep, a trunk or glovebox light, or an aftermarket accessory.