S9 MaxV Ultra vs Roomba j9+

Water tank is a numeric spec measured in ml. On this metric, higher values are generally better, but returns diminish past category-typical thresholds — going from a low value to a mid value usually matters far more than going from a mid value to a high one. When comparing two products, focus on the percentage gap rather than the raw delta: a 200-unit lead means something very different at the low end of the range than at the high end. Pay attention to the unit, too — manufacturers sometimes quote peak or burst figures that are not sustained in real-world use. Cross-check the published number against independent measurements where possible, especially for performance and battery claims. Finally, remember that a single spec rarely tells the whole story; the Mars Score weighs water tank together with the rest of the spec sheet so one outlier doesn't distort the verdict.