The safety guidance comes on Back to the Future day - the date Marty and Doc visited the future in the second of the three time-hopping films and discovered people riding hoverboards.
London Fire Brigade (LFB) said a rideable on charge in a bedroom in Southwark caught fire on 11 October.
Earlier in the month, a device exploded in Morden.
On 11 October, a transporter on charge in a bedroom in Southwark caught fire, causing a loud bang.
Charlie Pugsley of the LFB said: "The cause of both fires is still under investigation whilst the devices are tested at our lab.
"We'd urge people to keep an eye on their devices whilst they are on charge."
A fire service has issued a warning after two rideables - also known as 'hoverboards' - burst into flames.