My phone charges to 100% but dies after a minute or two

Hi, I have an iPhone 8 that is one year old. I started having battery issues where it would charge to 100% but rapidly deplete and die at high percentages. I called Apple tech support and they did a diagnostic over the phone. They said my battery’s life was 93% so they didn’t think I was having a battery issue. They did however say that there was something wrong with my wireless charging system (which I have never used) and that could be the culprit. I took my phone out of its case and realized the back was a bit shattered, it’s always been in an otter box so I never noticed. Now my phone stays at or around 100% but dies almost the moment I take it off the charger. I’ve been using a power bank and saving for a new phone. I’m pretty sure I’m done with Apple products for the foreseeable future. Is there a fix for my issue or is this phone scrap?