That dent may not phase most vapers, to be totally frank. It's not exactly large. With that said, I'm not going to advise someone to do something based on my own willingness to accept risk or not and it is most certainly true that more damage can be done internally than is visible.
I do find that if I am sitting there staring at a battery going "Is this safe" for whatever reason, it probably is an issue (for me) and for my own comfort and those of others, I just replace it.
LOL my own pet peeve is battery heat. As the husband was staring
vaping he would leave his gear out in the sun all the time in summer, in Tucson. To be fair, probably the same case could be made that using power tools in very hot weather is unsafe, and he does that all the time.
But there I would be, cackling at him at thermal runaway, and explosions and all sorts of stuff, which were probably Rather Unlikely. But we all have our "things" about
batteries, and as long as you are mindful of general safe practice and if you are unsure.... JUST RETIRE IT. For the price of a 6 or 7 dollar battery even a 10 dollar one, it's worth it for the extra safety and just OVERALL peace of mind. Plus then you don't have to think about it anymore, etc.
Good luck,
Anna