Charging System Check

Three measurements, three answers

Engine off you measure the battery state. With the engine at idle the alternator should push about 13.8–14.4 V. With lights, blower and radio on, the voltage should stay above 13.2 V.

• Engine off : 12.4–12.7 V healthy battery
• Idle : 13.8–14.4 V healthy charging
• Loaded : above 13.2 V healthy system
• Over 14.8 V : regulator likely overcharging
• Under 13.2 V : alternator or belt problem

Why this order matters

A weak battery can mask a failing alternator and a weak alternator can quickly kill a healthy battery. Measuring in the right order separates the two.