Sennheiser L 151-2

The L 151-2 charger can charge up to two BA 151 accupacks. The normal
charging time is 14 hours. We strongly recommend, however, to charge new or completely discharged BA 151 accupacks for 24 hours.
When an accupack is inserted into the charger, the corresponding LED lights up, indicating that the accupack is being charged.
The L 151 charger is powered via the supplied plug-in mains unit. Connect the plug-in mains unit to socket on the charger. Use the charger and the plug-in mains unit in dry rooms only.
Since the accupacks cannot be overcharged, they can remain in the charger even when they have been fully charged. However, when you are not going to use the charger for some time (e.g. when you are on holiday), you should unplug the mains unit and take the accupacks out of the charger.