The Roborock S8 MaxV Ultra lasts longer on a single charge: up to 180 minutes versus the Roomba j9+'s 120 minutes. Those are manufacturer numbers though, and your mileage will vary.
Real-World Runtime
The S8 MaxV Ultra has a 5,200 mAh battery. On normal settings with mixed flooring, expect 165-175 minutes per charge. That's enough for 3,000+ square feet in one go.
Crank it up to maximum suction (10,000 Pa), and you're looking at maybe 60 minutes. The powerful motor drinks battery fast.
The Roomba j9+ runs about 75-90 minutes in normal operation. That's enough for most average-sized homes, but larger spaces might need a recharge break.
Does It Actually Matter?
Both vacuums return to their dock, charge up, and continue cleaning. Even if your home is too big for one battery cycle, the vacuum eventually finishes.
Big home (3,000+ sq.ft)? The S8 MaxV Ultra's longer battery means fewer charging breaks and faster total cleaning time.
Average home (under 2,000 sq.ft)? Either vacuum finishes on a single charge. The battery difference doesn't affect you.
Using max suction often? The S8 MaxV Ultra's larger battery gives more runtime even in power mode.
The Fast Charging Advantage
The RockDock Ultra charges faster than the Roomba's Clean Base. If your vacuum pauses mid-clean, the Roborock gets back to work sooner.
For large homes needing multiple charging cycles, this adds up. An extra 15-20 minutes per charging break can mean the difference between finishing before you get home or not.
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How we researched this
Where this comes from: this answer draws on the product's published specifications and the reviews ShopSavvy collected for it, alongside prices from ShopSavvy's price data.
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