The jump-start test
Jump the car, remove the cables, and let it idle. If it stalls quickly, the alternator isn't charging.
The voltmeter test
A healthy battery reads ~12.6 volts with the engine off. With the engine running, a good alternator raises it to 13.8–14.6 volts.
Why professionals load-test
A battery can show 12.6 volts and still fail under load. A load or conductance tester tells the real story.
Frequently asked questions
Can a bad alternator ruin a new battery?
Yes — repeated deep discharges shorten battery life.
Do auto parts stores test for free?
Many do, but you'll need to get the car there.
Do you test both on-site?
Yes, every no-start call includes a battery and charging test.
Related services
- Mobile battery replacement — Battery testing, jump starts, and new battery installs.
- Mobile starter & alternator repair — No-start and charging problems fixed where you're stuck.
Need a mobile mechanic near you?
Our mobile mechanics can come to you today. Call 469-813-8778.