If you are brave and knowledgeable enough to replace faulty battery on your own you could be surprised that after all your patience, respect and careful work your phone just lost connection with message NO SERVICE or SEARCHing endlessly.
You will open your little gadget over and over again, clean all contacts, check all connections, wires, change even battery itself but WAIT.... there is simple solution for this.
CHECK your current date and time - it should be definitely something else that :
01. January 1970.
If this is the case - just try to change it to current, Save and RESTART the phone - MIRACLE!!!!
Everything is fine again, life is beautiful, friends are reachable.