All of a sudden iPhone 6 entered reboot loop

My phone has been working fine and then all of a sudden, as I was just playing a game, it reboot itself and is now stuck in a reboot loop. I tried entering recovery/DFU mode and I can get iTunes to recognize it. From iTunes I tried updating the firmware hoping that would resolve the issue but it fails with error 9 each time. I tried multiple different USB ports just in case but no luck. Each time it fails it gets as far as the screen showing the Apple logo with an empty progress bar under it.

I did not try any third party tools yet since I need to purchase them to try and not sure if that is the next best step. I didn't drop/damage the phone or replace any parts so it doesn't seem like something broke or got loose.

Any suggestions as to what else I can try? The battery on this phone was not in the best shape (it was still the original battery that came with the phone and would drain pretty fast). Could it be possible that it is a battery issue and replacing it may resolve the issue?

I am hoping to resolve this myself, otherwise I will take it to some repair shop.

Edit: I would like to preserve the data on the phone