Process · Diagnostics
How We Test a Car Battery Properly
Anyone can put a meter across a battery and read 12.4V. That number tells you almost nothing about whether the battery can deliver hundreds of amps to a cold starter. Proper testing measures capability under load, not just potential at rest.
We take four measurements and interpret them together: resting voltage after the surface charge settles, conductance or load performance against the battery's rated CCA, the voltage dip during actual cranking, and charging output at idle and at raised rpm with the electrics loaded.
Key points at a glance
- Resting voltage
- Settled reading with everything off
- Capacity test
- Measured cranking performance against rated CCA
- Cranking dip
- How far voltage falls while the starter turns
- Charging check
- Output at idle and about 2,000 rpm under load
What this means in practice
- A surface charge from a recent drive inflates resting voltage, so timing and interpretation matter.
- A deep dip during cranking indicates high internal resistance even when the resting reading looks acceptable.
- Charging output is checked with load applied because faults hide when nothing is switched on.
- We compare measured performance against the vehicle's required rating, not the battery's age.
- You get told the numbers and what they mean, so the recommendation is evidence rather than opinion.
Questions we get asked
Can you test without replacing anything?
Yes. A battery health check is a standalone job, and plenty of customers book one before winter rather than waiting for a failure.
How accurate are these tests?
Modern conductance testing correlates well with real cranking ability and is what the trade uses. Combined with a live charging check, it gives a reliable picture.
What if the battery passes but the car still fails?
Then the fault is elsewhere — charging, connections, starter or immobiliser — and we will point you at the right area rather than selling a battery.
Want the numbers, not a guess?
Book a mobile battery and charging test at home or at work.
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Category: Process, cost & aftercare · Our services · Battery replacement · Areas we cover