I have a two year old (set of?) MDR-1000X (the previous model) and the battery is still working fine. I usually have them on for 6 hours a day - with NC as it c

I have a two year old (set of?) MDR-1000X (the previous model) and the battery is still working fine. I usually have them on for 6 hours a day - with NC as it comes on by default, and I forget to turn it off - and only charge them once a week.