A flat voltage on an upstream (front) HO2 sensor would indicate a failed sensor putting the engine/transmission into a failsafe mode. It will not run with normal performance. Replace the bad HO2. If it is a downstream (rear) O2 sensors, it will just set a code and MIL, and not cause the ECU to enter a failsafe mode.
Since when you disconnect the battery you reset the ECU's learned fuel trims, shift points, and spark tables, it defaults to factory defined tables until they can be relearned.
Also, try resetting the ECU again by pulling the battery for a while again and disconnect the MAF sensor. Leave the MAF sensor disconnected. You will get an MIL and the engine will remain in open-loop mode, using only factory defined tables to maintain safe operation. Do not do this for an extended period of time (I've done it for about 20 miles before with no problem before I realized I forgot to reconnect it). Power should not drop off during this time.
I'm not sure exactly where based on the information given, but you have a sensor issue somewhere causing this problem.