Corded vs. cordless
Dolphin's Nautilus CC Plus impressed us with its cleaning power, and the anti-tangle cord worked as advertised.
There are advantages to having a corded robot vacuum, most notably not having to worry about recharging the device or about the lithium battery losing steam over time. Corded pool robots are recommended for most pool owners, because they're less prone to problems or to motor malfunctions. Corded robots also don't need to be pulled from the pool and recharged after each use, unlike all the cordless models on our list, with the exception of the Wybot S2 with solar charging dock.
That said, cordless robots are ideal if your pool isn't near an electrical power source. Running a long extension cord through the yard, in places prone to moisture, isn't advisable long term.
Cordless vacuums performed just as well as corded ones. We've been testing some of these cordless models for two years and haven't noticed a decrease in battery life.
Suction power and battery life
If you opt for a cordless model, consider the battery life and suction power along with the size of your pool. A larger pool demands a longer cleaning session, so it might be worth it to splurge on a pricier model with longer run time and more power. Power is measured in the gallons per hour, or gph, that the vacuum takes in. Lower-end models start at around 3,000 gph, with the best pool cleaners topping out at about 7,000 or 8,000 gph.
Filter type
Most robot pool cleaners will filter out the large debris, but the finer stuff requires a nanofilter.
All robotic pool cleaners should catch large debris such as gravel and leaves. To sift out finer debris and keep your pool water from getting cloudy, you'll need a nanofilter. Your pool's main pump and filter are meant to catch much of this finer stuff, but a powerful robot with a nanofilter will help.
Type of pool
The larger robotic pool vacuums we tested cleaned faster and had better suction than smaller models.
There are small pool robots designed for smaller above-ground and in-ground pools, and large robots made to handle up to 40,000-gallon pools on a single cleaning cycle. Depending on the size of your pool and the amount of debris that regularly ends up in it, choose a robot that can effectively and efficiently clean it in a single cleaning cycle. This is especially important to consider with cordless robots, since they'll need to be charged between each use.
There are pool cleaners made specifically for above-ground pools. They're typically smaller and less powerful, since they have less ground to cover. An above-ground pool cleaner should also be lighter, because it's more difficult to remove from the pool after use.
Sides and stairs
Brushing the walls and stairs of your pool manually doesn't require a ton of effort, so we didn't weigh those cleaning modes as heavily as we did floor cleaning.
About half the models we tested could clean the sides of the pool, and some even had modes to clean stairs. This is a nice feature to have, but brushing the debris on the steps or side of your pool down to the floor, where it can more easily be cleaned by the robot, typically takes no more than a few minutes. For that reason, we weighted the robot's ability to clean sides and stairs less heavily than its ability to clean a pool floor.
If you don't want to do even that small brushing chore before activating your robot, choose a model that has a side-cleaning mode.
Cost and value
Beatbot's AquaSense line has premium features and long-running batteries, but with price tags to match.
Reliable pool robots start at around $500 and go up to about $2,000. We found that robots between $700 and $1,200 were perfectly acceptable for cleaning a 25,000-gallon pool. Choose a robot above $1,200, and you're mostly paying for special features that aren't necessarily worth it.
For cordless robots, the battery life was superior on more expensive models, but the cleaning performance was often similar to that of less expensive vacuums.
Correction: An earlier version of this story mischaracterized suction power. It's measured in gallons per hour.
