Denver E-3400RM Manuel De L'utilisateur page 26

Refer to the battery lock and unlock, see the following pictures
for reference.
From the initial position 6 o'clock (where the battery and tube
is locked), insert the key into the key slot, and turn it
counterclockwise to position 12 o'clock
(Then the battery is unlocked).
On the contrary, you can unlock it.
Battery charge
If an AC outlet is available within reach of your bike, you can charge your bike directly with the battery
still attached to the bike. The charging port is covered by a plastic cap. Please open it then you will
find one port for charge directly.
Removing the battery is useful for charging in a location where the bicycle may not fit or when no
reachable AC power supply exists at the place where the bike is parked
Before removing the battery from the bike, you need to unlock as following steps:
* Turn it counterclockwise from 6 o'clock to 12 o'clock position.
* Remember to take off and care about the key after you withdraw from the battery!!!
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