2001 Stratus ES 4 Door Oxygen Sensor...

Hi,
I have a 2001 Stratus ES 4 Door 2.7 litre V6 Magnum and at 69540 odo. I just got a check engine light.
I ran the on-off diagnostics and I got first code p1684 (battery has been disconnected in the last 50 starts) and the error code p0140 (1/2 O2S Stays At Center).

What does this mean outside of "sensor 2 bank 1 remains outside of center"?

Do I need to replace this sensor?
If so can I do it myself?
how much should I expect to pay for the part?

Let me know...
Thanks

Oxygen sensors are supposed to vary their voltage between 0.1 volts to 0.9. Your sensor is stuck reading a specific voltage and not fluctuating. with 69,000 miles on it, it's not widely told, but it's good practice that @ 50,000 miles, the oxygen sensors are supposed to be replaced. The heat wears them down and causes them to act funny more down towards the road.