Chosen Solution
I performed a battery replacement with the iFixit repair kit. The battery works well, but the adhesive of one of the cells didn’t hold, and the battery is now rattling around inside my case. Oops… What should I do to fix it?
@mishchea some doublesided tape like this Tesa 61395 Tape or others that fit, strategically placed should be sufficient to hold it in place. Lots of room would lead me to some velcro which will make the next battery replacement easier :-)