What voltage is dead?

Resting under 12.2 V is low. Under 12.0 V is in trouble. Load testing is more honest than a resting number after a drive.

Windows lost auto-up.

Hold the switch up 5 seconds at the top, down 5 seconds at the bottom, each window. Common after a battery swap.

No. Repeated jumps punish the alternator. Test and replace.

Auto & Mechanics

Battery & Terminal Service

Test it, clean it, or replace it without wiping the radio

40 min6 photographed stepsBeginner

A complete battery job: resting voltage vs a real load test, disconnect order, cleaning corrosion, matching group size and CCA, bolting the hold-down, and the window-up relearn many cars need after a power loss.

What you'll learn

12.6 vs 12.2 vs 'it cranked yesterday'
Negative off first, on last
Why the hold-down bracket is not optional
Window and radio relearns

Inside this course

Test so you don't replace a good batteryA weak alternator looks like a weak battery if you only guess.
Clean or replaceCorrosion is acid. Treat it like acid.
Electronics after a power lossTake a photo of radio presets before you start. Memory savers help; they are not magic.
Take the old one backLead-acid is recyclable and often has a core charge.

Full step-by-step lessons with photos unlock with a subscription.

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First steps from Test so you don't replace a good battery

See how every step looks — photo, checklist, and pro tips included.

Resting voltage, not the number while the charger is hooked up.

01Resting voltage

Lights off, car off, ideally 30 minutes after driving. 12.6 V is full, ~12.2 V is half, under 12.0 V is in the ditch.

A battery that sat on a charger all night and still fails a load test is done. Auto parts stores often test free.

02Running voltage

Engine running typically ~13.7–14.7 V. Much lower and the alternator or belt may be the real story. Look at the belt before you buy a battery 'just in case'.

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