TechniSat DIGITRADIO 231 OD Manual page 104

The auxiliary battery cannot be charged in the DIGITRADIO 231 OD. To do this,
remove the battery from the DIGITRADIO 231 OD and use the original charger
from your battery manufacturer.
If the DIGITRADIO 231 OD is operated with an 18 V auxiliary battery or the mains
adapter, the boost mode is activated. With this the music power is 2 x 15 W.
> Close the battery compartment cover again by first inserting it at the bottom (4)
and then snapping it into place at the top (5) :
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