A dead or disconnected battery will clear the computer's engine memory Sergey, the tech is right that you'll need to drive it around that far to rebuild the memory. The engine will often even run rough for a while until it relearns all of the parameters it needs.
If the battery just went dead from lack of use, maybe it's still ok. I think I'd wait to replace the battery, or maybe have Pep Boys/Autozone just do a quick load test on it to see if it's ok.
