I have the same problem too. I cant seemed to charge my phone with my power bank. And its a hassle.
The first time I noticed this was when I was charging my phone (which still have 30% battery) and left it in my bag, the next thing you know, my phone was turned off and when I tried to turn it on, the phone battery was at 0% while it was still charging from the power bank! (The power bank has around 60-70% power)
I bought new cables thinking that it might be the cable’s problem. But I can use the cables elsewhere. But not on my power bank.
Tested it again a couple of times with numerous other cables. It can charge for a few second before the charging indicator turns off and the phone is not charging at all.
FYI-
Bought ip15 around 4-5 month ago (around Dec 2023 - got quite a hefty discount from my service provider and was put under 2 years contract)
Im not sure what to do and where to ask about this. Because iphones are expensive and not something that I can afford to buy even if its broken. But I need them for my work.
I upgraded my 7plus to 15 after nearly 5-6 years (i dont recall but it was ages ago)
Not sure if its only my phone. But Im posting and replying this here - maybe other ip15 users have the the same problem as well and can share if this is becoming a problem and apple should look into this and do something.