What is the difference between the Roomba i3 and i4?

Regarding the Roomba: The only real difference is the battery — the i4 has a larger battery that extends cleaning time, which matters for homes over 1,500 square feet. The i3 may need to recharge and resume on bigger floors, while the i4 can sometimes finish in one pass. If you don’t need the extra runtime, save money and get the i3.