iPhone shuts off at 100% battery
Hi, this morning I charged my new (since last month) iPhone 12 to 100%. Since I was at my girlfriends house, I used a kinda cheap charger, cause I left mine at home. I charged my phone in the night and when I turned it on in the morning it was fully charged. I used it for like 2 minutes and it shuts off. Battery empty. I charge it for a couple of minutes and the battery really is empty again. This is really frustrating can anyone maybe help me?
thank you in advance
iPhone 12, iOS 14