Battery swelling seems to be a common problem among these MobileStudios 13s, you could replace the battery but looking online they seem to cost anywhere from $90-$100 USD, if you do feel like going through with the battery repair, as long as you keep the battery level below 10% and take care not to puncture it, you should be fine.
It is totally your call if you feel that it is out of it's prime. $100 is a lot (in my opinion) for a tablet that is 7 years old and actively failing. But again it is totally your choice to make.