I have Roomba 650 for about 4 years. What a smart device!!! It is such a great help for an old man( I don’t consider 76- year- old man a very old, but my wife does). I don’t need to go on my knees to clean under the beds and couches anymore. Thanks, smart people! The only thing I modified is the hinge of the dust collecting unit door. I put 1/8 " stainless steel shaft from the day one of my purchase because I found it as a weak point. It looks like battery became weak because Roomba does not go to the charging station as it usually did. How can I be sure that my lovely helper needs a new battery?