The physical battery replacement went off without a hitch, and saw that the phone had no network connection, but also had no way to unlock. The slide lock said "Slide for Emergency Call" over my custom wallpaper and sliding would give the passcode screen, but it would reject the 6 digit passcode (it would buzz and go dark after the 4th digit, re-awakening and putting in the last 2 would indicate bad passcode). Very frustrating! I get it into recovery mode and convinced iTunes to "update" the OS, but it still didn't let me in. I performed a restore to fully factory reset the phone, and it worked! Sort of... the start screen kept being replaced by "Temperature - phone needs to cool down" but it's cold. Temp sensor is on the battery and returning to old battery fixed it. New battery is bad, and phone is wiped. Fun night.
I'm going to guess that disabling the password might save you from a similar fate. So, I'll suggest BEFORE YOU START, backup your phone and disable the passcode. Good luck.