Battery swapping wins when one site needs more than 4 hours of cleaning per visit. Below that, charging in place is cheaper and simpler. The crossover is glass area: roughly 1,200 m2 per site is where swapping starts to pay.
This is a boring topic that costs people real money. Teams buy a second battery because a salesman suggested it, then never use it. Others run out of charge halfway through a large roof and lose an afternoon. The deciding variable is how many square metres one visit covers.
How long does a robot actually run?
A typical skylight robot battery gives 2.5 to 4 hours of continuous cleaning, covering 500 to 900 m2 depending on dirt and speed. Charging back to full usually takes 2 to 3 hours. That gap is the whole problem: a big roof takes longer to clean than the battery lasts, and the recharge is long enough to end the day.
| Glass area per visit | Best option |
|---|---|
| Under 800 m2 | Charge in place |
| 800-1,200 m2 | Marginal, depends on schedule |
| Over 1,200 m2 | Swap batteries |
What are the hidden costs of swapping?
A spare battery costs 15 to 25% of the robot price, so it is not a trivial add-on. You also need a charging station in a dry, ventilated room and a safe way to carry the pack across a roof, which matters on steep or exposed sites. Batteries age whether you use them or not, so a spare that sits idle still loses capacity after three to four years.
The real risk with swapping is abuse. Hot-swapping a warm pack straight into a charger shortens its life. Let it cool for 20 minutes. Do that wrong for a season and you have killed your spare before it earned anything.
Which sites should never bother?
Single-site operators with moderate roofs should stay with charging in place and invest the money in a second robot instead if demand grows. Two machines covering 700 m2 each beats one machine with two batteries. On the Lingkong K3 this is the pattern we see most in mid-size atriums, where one charge covers the whole job.
If you are unsure where your site lands, measure the usable glass area, not the building footprint. Roofs look bigger than the cleanable panel. When in doubt, ask us to run the numbers before you buy a spare pack you will not use.
Key Takeaways
- Batteries give 2.5-4 hours, covering 500-900 m2.
- Swap when a visit exceeds about 1,200 m2 of glass.
- A spare battery costs 15-25% of the robot price.
- Let warm packs cool 20 minutes before charging.
- For small single sites, a second robot beats a spare battery.