Sandy, I just tested mine and at 9 hours it was still of running, but I think slower than before. It is about 5 years old, and is used regularly but this is not a professional setup, I work alone so over a 7 hour day in the workshop I am drinking coffee, using the bandsaw, sharpening tools, poking through wood stocks, or doing some other non turning activity for probably more than half a day.
Then at the end of the day I plug it in until the next time which may be tomorrow or may be 3 or 4 days away, and so far it hasn't exploded or otherwise harmed the battery.
Its about 6 or maybe 7 years old now, has used up quite a few filters but otherwise cost me nothing more than the purchase price.