Four fire engines and around 25 firefighters attended a fire on Barchester Road in Harrow.
Part of the first floor of a semi-detached house was damaged by fire. One man was treated by London Ambulance Service crews.
The fire is being treated as accidental and is believed to have been caused by the failure of a lithium-ion battery in a drill.
A London Fire Brigade spokesperson said: "Lithium batteries store a significant amount of energy in a very small space and are much more powerful compared to other types of batteries. If that energy is released in an uncontrolled way, then a fire or explosion may result. If there is overheating, crushing, penetrating or overcharging, then a fault can occur within damaged battery cells which may cause the battery to catch fire.
"Fires involving lithium batteries, which power devices, can be ferocious, producing jets of flame. The blaze is also hot enough to melt through metal. This type of fire produces a highly flammable, explosive and toxic vapour cloud which should never be inhaled. The fire can also be extremely challenging to put out. Our advice is to get away to safety and call 999.
"Lithium batteries, or the devices powered by these batteries, should be stored and charged in a location away from where people live, such as in a shed or a garage. If they have to be stored inside, make sure there is smoke detection fitted, it’s kept it in a room where you can shut a door and contain a fire and your means of escape is not obstructed. Never store or charge on an escape route such as a hallway or by an exit to a property.
"It is also important to ensure that you buy your batteries from a reputable seller and to ensure you are using the correct charger for the batteries."
The Brigade's Control Officers received around seven calls about the fire.
The Brigade was called at 1551 and the fire was brought under control by 1641. Crews from Harrow, Northolt and Wembley fire stations attended the scene.