Guide
Battery, starter or alternator? How to tell which one stopped your car
Dim lights and slow cranking point at the battery; bright lights and a single click point at the starter; a car that starts with a jump and dies again points at the alternator. A load test settles it, and that is the first thing a mobile mechanic does before replacing anything.
Updated 2026-08-22 · Frank's Mobile Mechanic 24/7
Battery
Slow, laboured cranking; dash lights that fade as you turn the key; a car that sat for a week or had the lights left on. A jump gets it going and it keeps running. Batteries also die of age — four or five years is a normal life in Valley heat.
Starter
Lights stay bright, you turn the key and get one loud click, or a whirr with no crank, or nothing; sometimes it starts on the third try or after a tap. The battery tests fine. That is the starter or its solenoid.
Alternator
The battery or charging light is on; lights dim at idle and brighten with revs; the car starts with a jump and dies again minutes later; a new battery keeps going flat. The alternator is not charging, so the car is running the battery down.
What gets tested
The battery under load (not just its resting voltage), the starter's current draw, and the alternator's output and ripple — in that order, because each result rules the next in or out. The estimate names the part that actually failed, and you approve it before it is replaced.
