I have a pair of "Ultra" brand 850mAh rechargeable batteries. They are nearly 10 months old I would guess and have been recharged nearly every 2 days. I also have a pair of 500mAh batteries that came with my headphones. Ok... The 500s still charge pretty fast and the 850s used to take about 2.5 hours, regularly. The 850s now take, well going on 7 hours at this time and still not ready. The charger is a usb, and still works based on the 500s. Is this pair of 850s at the end of their time. I already have more to take over but this is about life span.