Interactive voltage interpreter
12-volt battery screening chart
| Operating state | Screening band | What it supports | What it does not prove |
|---|---|---|---|
| Engine off, rested | About 12.6 V or higher | Well-charged state | Remaining CCA/capacity |
| Engine off, rested | 12.4–12.59 V | Partial charge | Battery failure |
| Engine off, rested | 12.2–12.39 V | Low charge | Why charge is low |
| Engine off, rested | Below 12.2 V | Very low charge / fault possible | Which component caused it |
| Minimum while cranking | Near/above 9.6 V at moderate temperature | Basic starter-load screen is reassuring | Battery CCA, cable loss or starter current separately |
| Engine running, conventional system | Commonly around 13.5–14.8 V | Charging support is visible | Maximum alternator current, ripple or smart-control behavior |
Temperature, battery type, recent charging, meter accuracy and intelligent charging control can move the readings. Vehicle-specific service information takes priority.
Read the chart as a sequence
1 — Resting
Start with charge state
If the battery begins substantially discharged, charge it before using crank voltage to judge capacity.
2 — Cranking
Watch voltage under load
A large sag can come from battery capacity, connections or starter load, so the number narrows the path but does not name the failed part.
3 — Running
Look for charging support
Compare with the engine-off baseline and account for smart charging before treating one running value as a fault.
Why 12.6 V is not a battery health certificate
Open-circuit voltage mainly reflects state of charge. A battery can reach a normal resting voltage but still have inadequate capacity when the starter demands current. That is why the focused battery test pairs resting and cranking readings.
Why about 14 V is not a complete alternator test
Running voltage shows what the system was doing at that moment. It does not measure maximum current output, cable voltage drop or alternator ripple. Use the alternator test for the multi-state procedure.
Source context
- Interstate Batteries — 12.6 V charged-battery context
- HELLA — battery/charging-system voltage context and intelligent regulation
- StartVitals methodology — full threshold logic and limits
Frequently asked questions
What does 12.2 volts mean with the engine off?
For a rested conventional lead-acid battery it indicates low charge. Charge and retest before deciding whether the battery has failed.
Is 13 volts enough while the engine runs?
It may be borderline in a conventional context, but modern controlled-charging systems can intentionally operate near battery voltage at times. Identify the charging strategy and compare with the vehicle procedure.
What matters more: resting voltage or cranking voltage?
They answer different questions. Resting voltage screens charge state; cranking voltage shows behavior under starter load. Use both when a starting problem is the concern.