I have an old Roomba 540 that was gifted to me after the original owner never used it. I'm not even sure how old it is, but it has yellowed plastic, it's held together with tape, and I think it's the 3rd battery. It just keeps going! I also replaced the brushes and dust bag/collector. I'm glad the replacement parts are easy to find because they do their job well even if they look pretty ugly. This new battery lasts a long time. My house is divided into different areas where I use Roomba (living room/kitchen, bedroom, basement, etc.). While I haven't done any runtime testing, I know it takes quite a bit of time to clean. . from different zones without discharge.
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