The KL 1208 makes a high-pitched whine. Solution: Normal. That is the switching transformer oscillating at 50-60kHz. If it screeches or clicks loudly, stop using it. The manual lists "audible coil noise" as acceptable only below 40 decibels.
For standard batteries, unscrew the screw-plugs and check the fluid level. Lead plates should be covered by at least 5 mm of distilled water. bosch kl 1208 battery charger manual exclusive
The guide has given you everything from LED decoding to thermal management secrets. This charger was built to last a decade or more, but only if you respect its quirks. The KL 1208 makes a high-pitched whine