Cordless is now the default in this category, and for most buyers it is the right default. There is no transformer to find a dry spot for, no cable to coil, and nothing that limits the robot to a straight-line pool shape. The machine goes in, it runs, it comes out.
The cost is a lithium battery working in warm chlorinated water for several hundred cycles. That is the single thing worth thinking hard about before you spend, and almost no review mentions it.
The battery question nobody asks
Ask two things before you buy any cordless robot. First: does a replacement pack exist? For the Aiper Scuba S1 and the WYBOT C1, third-party 8 Ah and 6 Ah packs are already on the market for roughly $70-80 — which turns a dead robot into a $75 repair instead of a $500 replacement. For several competing models, nothing exists, and when the pack goes the machine is scrap. We list what is actually available in the battery section.
Second: is the charger the failure point? In practice a $10 charger fails far more often than a $300 battery, and the symptom is identical — the robot will not charge. Before concluding you need a pack, swap the charger. The won’t-charge diagnostic runs through it in cheapest-first order.
Runtime versus rated area — read both
Manufacturers publish runtime in minutes and coverage in square feet, and the two are not interchangeable. A 90-minute robot rated for 860 sq ft (the Aiper Scuba SE) and a 160-minute robot rated for a similar area (the WYBOT C1) differ because the second one is moving more slowly and covering ground more thoroughly, or because it is also climbing walls. What you actually want is runtime long enough to finish your pool in one cycle. A robot that gets 70% of the way and parks is worse than a slower one that finishes, because the 30% it never reaches is always the same 30%.
The charging-dock models are a different product
The Aiper Scuba V3 and Obsidian ship with a wireless charging dock, and it changes ownership more than any other feature on this page. The robot returns to the dock, charges, and runs again — so the chore that actually stops people using their robot (lifting a wet 20 lb machine out, carrying it to an outlet, remembering to carry it back) disappears. If you have somewhere sensible to site a dock, it is worth more than most spec upgrades.
Where cordless is the wrong answer
- Pools over about 2,200 sq ft. Even the longest-running cordless unit here has to charge mid-job. A corded Dolphin never does — see the large-pool roundup.
- Daily-use or shared pools. A pack cycled every day ages in seasons, not years. Corded is the correct architecture for an HOA or rental pool.
- Buyers who want a ten-year machine. That is the corded list, and it is not close.
Winterizing a cordless robot
Store the pack at roughly half charge, indoors, above freezing. A lithium pack left flat in an unheated garage over a northern winter can drop below its safe floor voltage and refuse to take a charge in spring — which gets reported as “the battery died over winter” and is really a storage problem. Rinse the filter, dry it fully before it goes away, and keep the robot out of direct sun: UV embrittles the shell faster than chlorine does.
