I've had a phone with a swollen battery that I swear was not swollen when I chucked it in the drawer a year or two earlier. Apparently it's the battery itself breaking down that causes this, so I don't think any electrical protection scheme would necessarily help you.

I guess my advice is "don't use a really old and worn out battery for this". Otherwise it's probably fine? People walk around all day with one in their pocket and sometimes their ear after all.