A cordless window cleaning robot typically runs 60-90 minutes per charge, which covers roughly 80-140 m² of glass at 1.5-2 m² per minute. The cord was never the real constraint — battery weight and the lower suction margin are.
Cordless sounds like the obvious upgrade. It is not obvious at all. Cutting the cord removes a snag risk and a tether-management chore, and adds a battery that must carry suction pumps under load. Something has to give.
How much glass does 90 minutes actually cover?
Manufacturer throughput figures of 2-2.5 m² per minute are measured on a clean, flat, single pane. Real jobs run slower. Expect 1.2-1.8 m² per minute once you add edge approaches, corner turns, and a second pass on the dirty half of the pane.
- 60-minute battery: 70-100 m² realistically. One large commercial window wall, or two full runs on a domestic sunroom.
- 90-minute battery: 100-140 m². A small atrium, or a mid-rise floor of facade.
- Two batteries swapped mid-job: practical ceiling around 200 m² before you are really just managing batteries.
Compare that with a corded unit running off mains, which can work all afternoon on one connection. That is the whole argument, and it only holds when the job is bigger than a battery.
Does losing the cord reduce suction?
Often, yes — indirectly. The cord also carried power for the vacuum pump. On battery, the pump runs at a fixed budget the firmware has chosen to preserve runtime. Some cordless units hold 2,500-3,000 Pa against a corded unit’s 4,000 Pa or more. On vertical glass in dry conditions, that is fine. On wet, angled skylight glass at 35 degrees, it is the difference between a stable climb and a repeat alarm.
Ask for the suction figure measured with the wet pad fitted and the tank half full. Dry-glass suction numbers on a spec sheet flatter every machine.
Which jobs suit a battery machine, and which do not?
| Situation | Cordless verdict | Why |
|---|---|---|
| Domestic windows, 2-4 panes | Good fit | Under 40 m², one charge, no cable management |
| Sunroom / single skylight | Good fit if pitch < 30° | Short job, low height |
| Ground-floor glass of a shopfront | Poor fit | Corded is cheaper and unlimited on time |
| Full facade floor, 300 m²+ | Poor fit | Three battery swaps, suction margin risk |
| Steep glass roof above 40° | Avoid | Lower suction plus wet glass equals slip risk |
How should you charge a battery robot so it lasts?
Two habits extend pack life noticeably. First, do not store at full charge for long periods — 50-60% is better if the machine sits for weeks. Second, do not run to hard cut-off regularly; a machine that dies mid-pane at 4 metres is a safety event, not just an inconvenience.
Battery replacement is the hidden second-year cost. On a well-used unit, expect a new pack around 300-400 cycles. Price that in before comparing a cordless machine’s sticker to a corded one.
Is the app really necessary?
For a cordless unit, partly. Battery state, remaining runtime estimate, and error codes are genuinely useful on glass you cannot easily reach. Scheduling and voice assistant integration are not. If the app is the only place suction mode is adjustable, that is a design smell — you should be able to pick a wet-glass mode from the body.
Runtime claims are where spec sheets drift furthest from reality. Our logged runtime data for cordless units shows the gap on real panes, and our Lingfeng S1 review walks through a chassis built with kerb clearance in mind. For a broader comparison across brands, the window cleaning robot review archive covers units from several makers.
What should you check in the first ten minutes of ownership?
Run the machine on a ground-floor pane and time it on a stopwatch. Compare to the label claim. If a 90-minute machine gives you 55 minutes on a clean dry window at 20 degrees, the label is optimistic and the machine will be worse in the field. Return it inside the retailer window if you can — battery performance rarely improves.
Also check what happens at the end of a run. A good cordless unit parks and holds, or returns to its start point. A cheap one simply stops wherever it is. On sloped skylight glass, “simply stops” is not acceptable.
Key Takeaways
- Real coverage is 1.2-1.8 m² per minute, so a 90-minute pack does 100-140 m², not the spec-sheet maximum.
- Battery-powered suction often drops to 2,500-3,000 Pa versus 4,000 Pa corded — decisive on wet, angled glass.
- Cordless suits domestic and small skylight work; it loses on 300 m² facades and steep roofs.
- Plan a replacement pack at around 300-400 cycles and price it in.
- Time the first real run with a stopwatch before the return window closes.