Part of the ground floor of a mid-terraced house was damaged in the blaze in Thornton Health’s Beechwood Avenue around 7pm on Wednesday.
Four fire engines and around 25 firefighters rushed to the scene to tackle the fire.
It is believed to have been caused by the battery on an e-bike which overheated when propped against a radiator.
A child was taken to hospital by paramedics as a precaution and two women and three men were assessed on scene for smoke inhalation.
A conversion kit with a separate battery had been fitted to a normal road bike - a common cause of fires, investigators said, as many are sourced from the internet and may not meet safety standards.
Firefighters warned that batteries can pose a risk if they have been damaged, or exposed to extremes of temperatures, so users should try to avoid them being knocked around while in use or while being carried as spares.
They also advised users to unplug the charger once the battery is full, and advised against leaving it unattended or while people are sleeping.
Firefighters have issued an ebike safety warning after a house fire in #ThorntonHeath last night. The blaze was caused by an ebike and battery which were stored leaning against a radiator & they overheated. Be sure to follow our safety tips if you own one https://t.co/snWwkyCWdY pic.twitter.com/oT9wmwQqJu
— London Fire Brigade (@LondonFire) November 25, 2021
E-bikes can also block escape routes, said a Brigade spokesperson.
"Electric bikes and scooters are often stored and charged in escape routes in homes or communal areas so when a fire does occur, escape routes are blocked which immediately makes an already serious situation much more frightening for those involved so please do be mindful of where you're storing them,” said the spokesperson.
Firefighters were called to the blaze at 7.16pm and got the fire under control by 8.25pm.
Firefighters from Woodside, West Norwood, Norbury and Beckenham fire stations were at the scene.