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A6 Battery & Charging Spec Reference

The numbers you need at your fingertips for battery testing, SOC interpretation, and charging system verification. Includes temperature compensation, AGM vs flooded behavior, and field load-test pass lines.

State of Charge (Open-Circuit Voltage)

DEAD LOW FAIR FULL
< 12.06V
< 25%
12.06-12.24V
25-50%
12.24-12.45V
50-75%
> 12.45V
> 75%
100% SOC
Fully charged, stabilized
12.65 V
75% SOC
Minimum to load test
12.45 V
50% SOC
Recharge before testing
12.24 V
25% SOC
Deeply discharged
12.06 V
0% (cell damage likely)
Sulfation begins below 12V resting
< 11.90 V

Stabilize voltage 5-10 minutes after key off, or after a 1-minute headlight discharge to remove surface charge.

Carbon-Pile Load Test

Test load
SAE/BCI standard
½ CCA
Duration
15 seconds
Min voltage @ 70°F
≥ 9.6 V
Min voltage @ 50°F
≥ 9.4 V
Min voltage @ 30°F
≥ 9.1 V
Min voltage @ 10°F
≥ 8.9 V
Min voltage @ 0°F
≥ 8.7 V

Roughly subtract 0.1V from the 70°F spec for every 10°F drop. Battery must be at ≥ 75% SOC before testing.

Cranking Voltage (under start load)

Healthy cranking voltage (warm)
10.5 - 11.5 V
Healthy cranking voltage (cold)
9.6 - 10.5 V
Below 9.6V cranking, warm
FAIL — battery or cable
Below 8.0V — modules may reset
CRITICAL

Charging System (running)

Idle, no load
13.8 - 14.6 V
2000 RPM, full load
13.5 - 14.5 V
AGM compatible system
14.2 - 14.8 V
Smart charging (RVC/SOC-based)
12.5 - 15.0 V varying
Overcharge threshold
> 15.2 V — sense wire / regulator
AC ripple (DMM AC volts)
≤ 100 mV AC
Parasitic draw (after sleep)
≤ 50 mA

Flooded vs AGM

FLOODED

  • Charging window: 13.8 - 14.6V
  • Tolerates short deep discharges, slowly
  • Vented design — never seal
  • Replace ~3-5 years

AGM

  • Charging window: 14.2 - 14.8V (higher)
  • Deep discharge below 11.5V causes permanent capacity loss
  • Sealed, vibration-resistant, more expensive
  • Many systems require BMS reset after replacement

BAY-FLOOR RULES

Quick decision tree

  1. Battery surface charge? Wait 5-10 minutes or pull a 1-min headlight load before reading SOC voltage.
  2. SOC under 75%? Charge first. Loading a discharged battery just tests the charger.
  3. Charging output low (under 13.5V loaded)? Test sense-wire continuity to battery+ before condemning alternator.
  4. AGM battery installed in flooded-spec car? System will undercharge AGM. Always match battery type to vehicle spec or update regulator settings via scan tool where available.
  5. After replacing battery on modern car: Run BMS / battery reset procedure per service info. Without it, alternator may continue undercharging.