Runtime is energy divided by power
A runtime figure is a simple ratio. The numerator is the energy stored in the pack, in watt-hours. The denominator is the average power the machine draws while running, in watts. Runtime in hours equals watt-hours divided by watts. Everything else a datasheet says about runtime, whether it is a mode, a brush, a battery age, is a statement about one of these two numbers.
The energy follows from the pack data. Nominal voltage multiplied by capacity in amp-hours gives watt-hours. Cordless sticks typically use packs of 21.6-25.2 V with 2,000-4,000 mAh, per model datasheet; robot vacuums commonly carry 2,600-5,200 mAh packs. A 21.6 V pack at 2,500 mAh stores 21.6 x 2.5 = 54 Wh. A 25.2 V pack at 3,500 mAh stores about 88 Wh. Divide by the power draw and the runtime follows: 54 Wh at 100 W lasts about 32 minutes, at 200 W about 16 minutes, and at 50 W about an hour.
What typical runtimes look like
| Type | Typical pack | Typical range across the category | What drives the spread |
|---|---|---|---|
| Cordless stick | 21.6-25.2 V, 2,000-4,000 mAh | 30-60 min | Mode, motorised head, filter load |
| Robot vacuum | 2,600-5,200 mAh | 90-180 min | Suction level, mopping, floor type |
| Handheld | 7.4-14.8 V | Per model datasheet | Size of pack, small motor draw |
| Cordless car vacuum | Small pack, or 12 V cord alternative | Per model datasheet | Pack size and tool load |
The spread inside each row is wide because the same pack can run very different loads. Figures are orientation for sourcing conversations, not promises for a model.
Mode and brush: the two big levers
The motor in a high mode may draw several times the power of its eco mode. A stick that lasts 45 minutes in its lowest mode may last 10-15 in maximum. The motorised head adds its own load, and a brush working through carpet draws more than one gliding over a hard floor. Loaded filters and a full bin raise airway resistance, and on many designs the motor then draws more or less depending on its control strategy. For this reason a runtime claim should be given for each mode, with the brush state stated. A single number tells you only that the plant has chosen the most favourable case.
Many sheets also quote runtime with the brush off. That figure is valid for a handheld use case but misleading for a floor machine. If the target customer is a household with carpet, ask for the runtime in the mode they will use, with the floor head fitted and running.
Why real runtime is below the arithmetic
- Usable capacity. A battery management system cuts off before cells are fully drained, to protect them. Usable energy is lower than the nominal figure.
- Current effects. High discharge currents reduce the energy a cell delivers; the voltage sags, and the pack is empty sooner than the label suggests.
- Temperature. Cold cells deliver less; hot cells age faster and may trigger thermal protection.
- Age. After many cycles the capacity of a pack falls. Runtime for a new battery says nothing about its second year.
- Conversion losses. The motor controller and the motor are not perfectly efficient, which is why motor type matters; see brushless vs brushed motors.
So the arithmetic is an upper bound. A reasonable working rule is to verify by test rather than by calculation: a runtime figure is only credible if the method is stated, the battery was new or aged to a stated cycle count, and the starting charge was full.
Charge time and pack design
Runtime is paired with charge time. A bigger pack gives longer runtime but longer charging with the same charger, so the charger rating and the pack capacity must be chosen together. Many brands add a second, swappable battery for professional users, or choose a fast charger at the cost of cell life. Pack design is also a regulatory matter: cells are typically 18650 or 21700 lithium-ion, and the pack passes UN 38.3 for transport and IEC 62133-2 for safety, with UL 2054 or UL 62133 for North America, with a BMS on board. The vacuum battery pack page lists the six parts of a typical pack, and the note on lithium rules in shipping is part of the sourcing series. These are routes a partner plant follows, and the documents are verified per project.
Robots and the long-runtime case
Robot vacuums run on the same arithmetic but with different habits. Their motors are small and the suction level is selectable, so the pack lasts 90-180 minutes in a typical range, and the quoted figure is again tied to the lowest or standard level. Two additional factors apply. First, mopping modules and pumps draw extra power, so a vacuum-and-mop cycle runs shorter than a vacuum-only cycle. Second, the useful number for the owner is often coverage rather than minutes: how many square metres of floor can be cleaned on one charge before the robot returns to the dock and resumes. That depends on navigation efficiency as much as battery capacity. A sheet that gives both minutes and coverage, with the floor type and mode, is more useful than one that gives minutes alone. The robot vacuum cleaner line page lists the typical battery options.
For the supply side, transport of the pack is a separate topic. Sea and air shipment of lithium cells and packs follows the UN 38.3 test summary and carrier rules, covered in shipping cordless vacuums.
What to put in a runtime specification
- Pack voltage, capacity in mAh and the resulting Wh.
- Runtime per mode, with the motorised head fitted and the brush running.
- Test method: new pack, full charge, floor type and the stop criterion.
- Charge time with the supplied charger.
- Cycle life or capacity retention expected after a stated number of cycles.
- Spare battery availability, since packs are the most requested spare part.
With these, a runtime claim can be reproduced by an inspector and compared with the sample report. Read how the sheet fits together in how to read vacuum specs, or see the cordless stick vacuum line for typical options. Pack quantities are counted in thousands for component orders; see MOQ and lead time, or send a target to the desk through the quote form.