iPhone Boot Issue

[eli_cook19]

So, one of my friends had an iPhone 6 Plus with a terrible battery. I had a spare iPhone 7 Plus battery that I didn't need. So I installed it and everything went fine, I replaced the battery and it worked. We decided not to tape the battery down and because the iPhone 7 Plus had to accommodate for the taptic engine the battery was shorter than that of the 6 Plus. It turned on and worked just fine for the rest of the night but it trickle charged and eventually started losing power on the charger and died. The battery moved so much that it broke free of the ribbon cable. So I put another battery in and when I power on the iPhone it shows the Apple logo for a few seconds, then the LCD goes black (but remains on for about a minute or so before turning itself off). It feels like it doesn't pass POST or something. I plugged it into iTunes and tried updating it, but it gave me error 26. If anyone could help me out with this at all it is greatly appreciated.

[DrMacintosh]

Error 26 is associated with corrupted data on your boot volume. You'll have to enter DFU mode and restore the phone.