Two to three years is typical for robot vacuum batteries.

About two to three years, sometimes a bit longer, before you’ll really notice it struggling to finish a cleaning run.

Mid-range bots (say, $300 to $600) use lithium-ion batteries good for roughly 500 charge cycles. If you run it daily, that’s about a year and a half. But most people don’t run them every single day, so two to three years is the realistic window. Degradation is gradual: first it can’t do the whole house on one charge, then it starts dying halfway through the kitchen. By year three you’re probably manually docking it more than you’d like.

A few things can speed it up: always running it until dead, storing it in a hot garage, or using a cheap knockoff charger. But even with perfect care, the cells wear out. Replacing the battery is usually doable (often $40–$60 and a screwdriver), but by year three the robot itself might be showing its age in other ways.

If you’re buying used, assume the battery is already degraded—factor in a replacement cost. If you’re buying new, just plan on year three being when you decide if it’s worth fixing or replacing.