330 battery got a lower power and it is not for sale. The one on sale at the website is of higher capacity~
So if you put in tat higher capacity battery, your 330 would run the same distance as 350~
Allow me to correct some misconception regarding different models.
Scooba 330 main body IS in fact same as 340 (the rare special model rated for 850 sq ft).
340 (introduced in 2007) was a specially bundled model which came with high capacity battery & round silicon mat. 340 has same physical structure as 380, except it's blue theme while 380 is grey theme. 380 also came with external battery cradle & 2nd Virtual Wall.
The 1st gen 5800 (introduced in 2006) was heaviest & slowest (same as 5900 which can't run on plain water).
Some time in yr 2008, 5800 became medium weight & medium speed, its physical structure was like 350 (rated for 500 sq ft).
In yr 2009, 330 was introduced. It's the latest 5800 (iRobot use the code 330 & 5800 interchangeably). 330 as stated above, is in fact 340 except it's low capacity battery. It's as light & fast as 380, so a high cap battery upgrade would give 850 sq ft.
350 (the 500 sq ft model) already came with high cap batt, but due to its medium speed & medium weight, it cannot achieve 850 sq ft.
Tank capacity for all Scooba models are the same, the design of the pump is the thing that determines rate of water usage. 380/340/330 all have a pump rate control sensor that regulates speed for water dispensing.
Any difference in brush motor power? Answer is... it depends when it's manufactured.
Earlier versions of scooba had a larger brush motor, newer versions have a smaller brush motor. Why? Perhaps it's cost cutting, perhaps it's change of vendor.
Then why does iRobot say 330 is for 250 sq ft?
Low capacity 3000 mAh battery = 1 tank = 250 sq ft
High capacity 4100 mAh battery = 2 tank = 850 sq ft
So... 37% more battery power gives >300% cleaning power. Do the math... Something doesn't add up.
For 330 to lose out by that much, it needs to be REALLY heavy & REALLY slow. But any user who have handled 330 before would know it's very light & very fast.
I have handle ALL Scooba models before (5900, 1st gen 5800, 2nd gen 5800, 330, 340, 350, 380, 335). So I know!
iRobot downplay 330 so that they can continue selling 350 & 380 at higher price.