Automotive Service Excellence (ASE) A6 Electrical/Electronic SystemsBattery Diagnosis and ServiceMedium
A technician is connecting a battery charger to a vehicle battery that is still installed in the vehicle. After connecting the positive clamp to the positive terminal of the battery, where should the negative clamp of the charger be connected?
- ATo the negative terminal of the starter motor.
- BTo a clean, unpainted metal part of the engine block or chassis, away from the battery.
- CTo the positive terminal of the alternator.
- DTo the negative terminal of the battery.
Show answer & explanationAnswer & explanation
Correct answer: B. To a clean, unpainted metal part of the engine block or chassis, away from the battery.
When charging a battery installed in a vehicle, connecting the negative clamp to a clean, unpainted metal part of the engine block or chassis, away from the battery, minimizes the risk of a spark igniting hydrogen gas that may be venting from the battery. The final connection (negative) is where a spark is most likely to occur.
Why the other options are wrong
- A. While the starter motor is grounded, the engine block or chassis offers a more general and often safer grounding point away from fuel lines or other sensitive components.
- C. Connecting to the alternator's positive terminal would create a short circuit as it's a positive connection, not a ground.
- D. Connecting directly to the negative terminal is generally done for batteries removed from the vehicle; it's less safe when installed due to potential sparks near gas.
Battery Charger Connection Safety
The correct and safe procedure for connecting a battery charger to prevent sparks, electric shock, and potential explosions, especially when the battery is installed in a vehicle.
- Connect positive to positive first
- Connect negative to ground away from battery (if installed)
- Connect negative to negative (if battery removed)
- Turn charger OFF before connecting/disconnecting
Memory trick: Positive first, negative far, keeps the sparks afar.