I just completed replacing the front and back , front broken, back just scratched and ordered a replacement battery as wellas run time had decreased significantly in 2.5 years.
May as well make the 4s look new again
I experienced ALL the symptoms listed previously, searching and the like but none of the remedies worked for me!
I noticed that it would go to Apple screen, off, then recycle over and over but when connected to my iPad charger it would eventually get to the home screen,...DISPLAYED 100% and still charging?".
Since nothing else worked, I decided to try putting the old battery back in and,,,IT WORKS!
In my case a defective new battery was the cause!
Strange but true!
Thought I[d pass it along to maybe benefit others as I suspect it was erroneously displaying 100% then shutting down due to lack of power.
Odd that it had the same symptoms though. 1 other thing, my date was also off, back to Dec31, 1970 but my WiFi was greyed out and could not select.
Maybe I should have treated like my old Cube, 1 mod at a time!
Just didn't consider a new back and battery could cause such problems.