Four fire engines and around 25 firefighters tackled a fire at a block of flats on The Concourse in Colindale.
A room in a fourth-floor flat was partially damaged by fire. Most of the rest of the flat was damaged by smoke. There were no reports of any injuries.
The fire is being treated as accidental and believed to have been caused by the failure of a lithium-ion battery for a power bank.
A London Fire Brigade spokesperson said: “Lithium batteries are susceptible to failure if incorrect chargers are used, so it’s important to always use the correct charger for the product and buy an official one from a reputable seller.
"You should unplug your charger when you have finished using it and we would advise not to leave it unattended or charging while people are asleep.
“Batteries can present a fire risk if they’re over-charged, short circuited, submerged in water or damaged, so it’s really important to protect them against being damaged too.
“Try to ensure they are not getting knocked around while in use or while being carried as this can increase the chance of damage to cells."
The Brigade was first called about the fire at 1406 and Control Officers mobilised crews from Mill Hill, Hendon, Finchley and surrounding fire stations to the scene. The fire was extinguished by 1601.