The NAO battery is declined in several versions.
To determine the version, refer to the serial number indicated on the battery.
Where is located the battery serial number ?
First, you need to access the battery to remove it from the robot. Follow the instructions here.
When the battery is removed, look at the lower section of the sticker and read the serial number :
How to read the serial number ?
The battery serial number can be read as followed :
For the battery in the picture, the serial number is ALDE000398 B 03 029926.
Meaning that its version is B03.