SIMs can't be formatted. I'm thinking your SIM is not damaged, but possibly dirty. Try removing it and wiping the contacts off (do not use cleaner, could eat the card). They (SIMs) contain vital phone identification information that will help your phone connect to the LTE towers.
Originally Posted by pfunkski
From my experience, it's normal from a fastboot to dump into recovery so you can do a full factory data/cache wipe.
Here's what I recommend, try using an original DroidUtility to re-fastboot your phone now that the battery is working and charged. Do a FULL WIPE on cache, data, battery stats, as much as you can from the DroidUtility. Sounds like there's something left behind from the bad flash making your phone retarded.