Remnants of a burned out phone after it caught fire on an aircraft Remnants of a burned out phone after it caught fire on an aircraft

Cheap battery chargers may be to blame for the growing number of lithium-ion battery fires in mobile phones.

Here we explain why they can cause the phone to overheat going into what is known as thermal runaway which is a rapid, uncontrolled chemical reaction within the battery that causes the internal temperature to rise. When one cell in a battery overheats it can produce enough heat - up to 900°C (1652°F) - to cause adjacent cells to overheat. This can cause a lithium battery fire to flare repeatedly which is a real concern when it happens on board aircraft.

According to Aviation Weekly, correctly designed and manufactured batteries contain management and “thermal interrupt” circuitry designed to prevent runaways. However, faulty chargers can compromise these built-in protections. Use of chargers not matched to devices like mobile phones has been known to be bypass battery-management circuitry, causing thermal runaways.

According to Louisa Fisher, cabin safety manager at FlightSafety International, inexpensive charging equipment for brand name devices has become a frequent source of thermal runaways in digital equipment.

She said: “Something left unattended on a charger can overheat and catch fire or damage the device that’s being charged. There is a great concern about using these off-market charging devices on quality equipment that they weren’t designed for.”

* Lithium-ion battery fires can be particularly dangerous on aircraft which is why more than 50 airline companies across the world – including some of the biggest and best-known - now carry AvSax fire containment bags to deal with fires in personal electronic devices caused by lithium-ion batteries that power them.

The bag – which won the Queen’s Award for Enterprise this year - has been used 27 times to deal with emergencies since the start of 2017.