Littlemadi

I have an automower 315. It has 1016 hours on it. For months it has been working great, it would cut for about an hour, then charge and cut for about an hour again just like expected. The last couple of weeks it seems to be cutting for a shorter amount of time. This morning after charging all night it cut for only about 30 minutes and then headed back into charge. I have done research and the batteries usually last much longer than 1000 hours. Any ideas?