Follow this sequence to ensure you don't damage the charger or your battery.
Humming Noise: A slight hum is normal operation for the internal transformer. Technical Specifications Input: 230V AC / 50Hz Output: 6V / 12V DC Charging Current: 6A (Effective) Battery Capacity Range: 20Ah to 120Ah bosch kl 1206 user manual new
Set the Voltage: Toggle the switch on the KL 1206 to either 6V (motorcycles/vintage cars) or 12V (standard modern cars). Follow this sequence to ensure you don't damage
Ensure the charger is unplugged from the wall before connecting to the battery. Understanding the Interface Ensure the charger is unplugged from the wall
Charger Gets Hot: It is normal for the unit to feel warm, but if it smells of burning plastic, unplug it immediately.
Should you need to find an original PDF copy of the Bosch KL 1206 manual, I can help you or find replacement fuses for your specific unit.