You can assign batteries within groups by following the next steps:
Head to Battery Storage and click Groups
Select the group you want to assign devices with
Scroll down the Group view until you see a button called Connect Stations. Now click it.
All available batteries are now opened up in a table. Click Connect to assign batteries in the group
The batteries connected to the group are displayed in the table called Connected Stations
The changes are automatically saved whenever a battery is connected to the group or disconnected from the group