You may want to check the following page:
Kobo Libra 2: Pleasantly Repairable for some information. There are a lot of other links plus you can also check the iFixit guides for the Libra Colour (
Kobo Libra Colour (N428) Repair ) since opening up most of the Kobo ereaders is pretty similar.
In the attached image, you can see where the Libra 2 battery is soldered to the motherboard.