The Roomba i4's bigger battery is the only real difference from the i3

If you’ve ever squinted at two nearly-identical Roomba models trying to figure out what you’re actually paying extra for, the i3 and i4 are a case study in minimal differentiation. They use the same smart navigation, the same suction motor, the same brush system, the same dustbin — everything is identical except the battery.

The i4 packs a larger battery that extends cleaning time by a meaningful margin, which matters if your floor plan runs larger than 1,500 square feet. The i3 will need to recharge and resume on bigger homes; the i4 can sometimes finish in one pass. That’s the entire difference.

It’s refreshingly transparent from iRobot, honestly. Most product lines bury distinctions across five different model numbers with minor software gating. Here, the answer is literally “bigger battery, cleans longer.” If you don’t need the runtime, save the money and get the i3.