Pull out the connector, be careful and only pull the connector and not the wires to avoid damaging them in the process.

The battery is fixed in place with double sided tape. Make sure not to bend and damage the battery when taking it out.

Text on the battery:

Grand-Pro

- PL805050 3.7V 8.14Wh

GB-GP004 UN38.3 2200mAh

+ 11-22-2014-11265