Mine is about 5 years old
I have a D10A. The battery is about 5 years old and when I tested it today, it lasted about 5-10 mins and shut off. So I guess I will buy a new one. I have not been vigilant about checking the battery regularly, so I don't actually know how long it has been bad. It did work last summer (2014) for at least 15 minutes when I was flying without ships power.
Just another data point.