There are a few YouTube videos of teardowns of other Kobo models. Although the precise configuration of the Aura HD might be somewhat different, the videos can give you a good indication for what is involved in the process.
Towards the end of the first video, it shows the person removing the battery and will give an indication of how firmly they can be glued in place.
https://www.youtube.com/watch?v=2SmYg4q9ai4
https://www.youtube.com/watch?v=bffxKvz9RhA
I had to replace the battery on a cheap tablet. Couldn't find any instructions or videos for the make I had. However, watching videos of how people replaced batteries in a variety of other tablets was very informative and allowed me to successfully complete the task on a tablet which I would have otherwise junked.
Best of Luck.