If this is for your Crown Vic or Mustang, FORDs seem to not have a lot of oxygen sensor failures. The originals are rated for 100K miles, and should be good for longer.
I changed my upstream sensors at about 160K miles, and it made no difference.....motor ran great before and after, no change in fuel economy.
Usually oxygen sensor codes are for something else that is causing the code.....lean codes most commonly being caused by a vaccum leak (air leaking into the intake that the MAF does not get to measure).
Having said this....having BOTH sensors fail at the same time is even less likely.
I would clean the MAF, clear the codes, and see what happens.
On my FORD, it took longer than mentioned to drain the charge when discharging the electrical system.
What I have done is to have the headlights turned ON when I disconnect the battery terminal......5 minutes later, reconnect.
HOWEVER, if you have a code reader, many of those have a function to clear the codes, and I would do that if yours does.
In the UNLIKELY event that you need to replace the oxygen sensors, I would buy the Motorcraft brand.
I also like to replace both of the upstream sensors together so that you have better matched switching charactoristics between the 2.
I have read that the switching speed slows down as they age, which is why I changed mine, but it was not needed.
The computer monitors the switching speed, and if they get too slow, it will light the CEL and set a code that specifically states that the switching speed is too slow.
Downstream is not so important as they switch slower due to the monitoring that they are doing (and only serve to tell the computer that the catalytic converters are working).