Why is my iPhone overheating after replacing the screen?

My screen was broken so i bought a replacement screen off of eBay. While repairing it, I damaged one of the connectors leading to the home button, so I had to replace the metal shield, which took a few days to arrive, so I used the phone without having a functioning home-button for a while.

During this time, the phone overheated while charging and even during extremely light usage. Also, my battery will last only about an hour of usage or a day of standby time. In settings it says the App Store used 67% of the battery the last 24h, with 1 min onscreen time and 4,9h background activity. The heat seems to be coming from the CPU I believe...

At first I thought maybe it was because of a bad/cheap lcd so I bought an LCD which seems to be OEM but repaired as the screen has some bright spots compared to the rest, but this didn't solve the problem.

Today, the metal shield arrived and I repaired my phone again, gaining the home button and touch id function, but without solving the overheating problem.

All help is welcome

Note: I installed the newest iOS 10 developer beta today, but the phone has been running developer betas (iOS 10) ever since thy came out and it has been working fine before the screen replacement.