A cordless window cleaning robot in 2026 runs 20-45 minutes per charge and holds 1,800-2,800 Pa on smooth glass. The corded machine still wins on sustained suction; the cordless wins where there is no socket within reach.
Every buyer wants cordless until they see the numbers. Then half of them go back to a cord. Let me save you the round trip.
What runtime can you actually expect?
Marketing says “long battery life.” Reality: a 2,000 Pa machine pulling hard on glass drains a 3,500 mAh pack in about 25 minutes of continuous climb. Real-world clean time is less, because the robot pauses at edges and re-seats its suction. A typical home window, maybe 1.5 square metres, takes 6-10 minutes. So one charge does two to four windows, not a whole building.
| Factor | Cordless | Corded |
|---|---|---|
| Runtime / reach | 20-45 min | Unlimited |
| Suction stability | Drops as battery drains | Constant |
| Best for | High windows, no socket | Long runs, flat glass |
| Cable / fall risk | Fewer snag points | Cord can tangle tether |
Why does suction drop as the battery drains?
The vacuum pump is the biggest current draw. As voltage falls, the pump spins slower and vacuum decays. On a flat window you will not notice. On a 25-degree skylight, a machine that held at 100% battery can start slipping at 30%. That is the moment robots fall. If your glass is sloped, either buy a corded unit or keep the cordless above 50% for slope work. This is exactly why Lingdu Intelligence splits models by slope rather than pretending one battery machine climbs everything.
When is cordless the right call?
Buy cordless when the glass is far from power: upper-floor windows, glass roofs over a stairwell, atria where running a cable is a trip hazard, or heritage buildings where you cannot clamp a cord. The freedom is real. Also buy cordless if the alternative is a ladder, because a fall costs far more than a spare battery.
Skip cordless if you clean long horizontal runs where constant suction matters, if your glass is steep, or if the site has a ready socket at every bay. And always keep a charged spare battery; a half-charged cordless on sloped glass is a dropped robot waiting to happen. For slope guidance, see our skylight spec guide.
What about the safety tether on a cordless machine?
Still mandatory. Cordless removes the power cable, not the fall. Clip the tether to a rated anchor every single run. Battery machines are lighter, which helps retrieval, but they still hit hard from three storeys up.
Key Takeaways
- Cordless robots run 20-45 minutes and cover 2-4 typical windows per charge.
- Suction decays as the battery drains; on slopes keep it above 50%.
- Buy cordless for distance from power or ladder replacement, corded for long flat runs.
- Keep a spare charged battery; it is cheaper than a dropped machine.
- The safety tether applies to cordless machines too.