How much electricity does a cordless vacuum use?

The simple sum: volts times amp hours

A battery's stored energy in watt hours (Wh) is its nominal voltage (V) multiplied by its capacity in amp hours (Ah). If capacity is given in milliamp hours (mAh), divide by 1,000 first to get Ah. Divide Wh by 1,000 to get kilowatt hours (kWh), the unit on your electricity bill.

Charging is not perfectly efficient. Some energy is lost as heat in the charger and battery. Our battery energy calculator uses an editable default of 85 per cent charger efficiency, so the energy drawn from the wall is the battery's Wh divided by 0.85.

• Battery energy (Wh) = volts x amp hours
• From mAh: Ah = mAh / 1,000
• kWh = Wh / 1,000
• Energy drawn from the wall = kWh / charger efficiency (for example 0.85)
• Cost per charge = kWh drawn x your unit rate in pence per kWh, from your own bill

Worked examples

Makers often list voltage but not capacity. Where both are stated we use them; where capacity is missing we use a clearly labelled illustrative figure. The Bosch Unlimited 7 listing gives both: 18 V and 3.0 Ah per battery pack, with two packs supplied. That is 18 x 3.0 = 54 Wh per pack, or about 0.064 kWh drawn from the wall per full charge at 85 per cent efficiency.

The Shark Stratos Pet Pro lists 25.2 V, and the Shark PowerPro and Dyson V8 Advanced list 21.6 V, but these listings do not state capacity in Ah. So for a 25.2 V machine we use an illustrative capacity of 2.8 Ah: 25.2 x 2.8 = 70.6 Wh, or about 0.083 kWh drawn from the wall per charge. This is an example only, not the Stratos battery's stated capacity. Check the label on your own pack for the real figures.

What that means over a year

Using the illustrative 0.083 kWh per charge, charging four times a week comes to about 0.083 x 4 x 52 = 17 kWh a year. Charging every day comes to roughly 30 kWh a year. Those totals are small next to appliances that heat water or air. Your figure depends on your battery, how often you fully drain it and how efficient your charger is.

To turn kWh into money, multiply by the unit rate shown on your bill. We do not quote a rate because tariffs differ and change. The battery energy calculator lets you enter voltage, capacity, charges per week and your own pence per kWh to see a per charge and per year figure. The Energy Saving Trust has general advice on reducing household electricity use.

Work out your vacuum's energy use →

Charging times from listings

Charging time depends on battery size and charger output, not on how much energy the battery uses in cleaning. A longer charge time does not mean more electricity; it usually means a lower power charger. These are the charge times stated in product listings:

The Dyson V15 Detect Animal listing does not state a charge time. Check Dyson's current specification for your version. As a general rule, Dyson's larger V-series batteries take several hours from empty. A partly used battery charges faster than a fully flat one.

Docks, Clean Stations and standby

Most chargers draw a little power while plugged in even when the battery is full, and a wall dock that keeps the vacuum topped up adds a small standby load. The amount is usually tiny compared with the charge itself, but it runs around the clock, so it adds a little over a year. If you want to avoid it, unplug the charger once the battery is full, as long as your maker's instructions allow this.

Self-emptying stations, such as Samsung's Clean Station with Air Pulse on the Bespoke Jet Plus Pro Extra, use a powerful motor for a few seconds to empty the bin. Each emptying cycle is short, so the energy per use is small, but it is extra to the battery charge. For more on these, see our cordless vacuums with self-emptying dock guide.

Note:Use only the charger or dock supplied by the maker, or one the maker approves for your model. Do not charge a damaged or swollen battery, keep chargers away from water and heat, and stop using the charger if it smells of burning, then contact the maker or a qualified repairer. Recycle old batteries at a battery recycling point, never in household waste.

Frequently asked questions

How long does it take to charge a Dyson V15? The V15 Detect Animal listing does not give a charge time, so check Dyson's current specification for your version. Dyson lists 4.5 hours for the V8 Advanced and up to 5 hours for the V8 Origin, which gives a sense of scale for V-series batteries.

How long does a Dyson V8 battery take to charge? The V8 Advanced listing gives 4.5 hours and the V8 Origin listing up to 5 hours from empty. A partly used battery charges faster.

Is it cheaper to use a cordless or corded vacuum? Both use small amounts of electricity in household terms. A cordless battery stores well under a tenth of a kWh in our examples. Work out your own figure with the battery energy calculator and your unit rate.

Does leaving a vacuum on charge waste electricity? A charger or dock draws a small standby amount once the battery is full. It is minor, but unplugging when full saves it if your maker's instructions allow.