Mobile phone being charged. Photo by Daniel Korpai on Unsplash Mobile phone being charged. Photo by Daniel Korpai on Unsplash

People may be shortening their phone batteries’ lifespan by overcharging them … simply by leaving them plugged in overnight.

Many mobile phone users simply plug them in and switch the power on when they go to bed and then wake up to them 100% charged. The trouble is, they’ll have been 100% charged for hours and constantly doing this will damage the battery.

And there is always the danger that if they overheat – perhaps if they are beneath a pillow – they could catch fire, sparking a house blaze with potentially tragic consequences.

Dominik Schulte, managing director of Germany-based battery technology consultancy firm BatterieIngenieure told news website Business Insider: “If you're going to charge your phone to 100% and keep it at 100% — just keep on charging and charging overnight — this will have negative influence on aging. It would be very good to charge the phone in the morning or whenever, but don't store the phone overnight at 100%." 

The website Android Authority says it’s best to just partially charge your phone.

Reporter Robert Triggs states: “One particularly persistent battery myth is that you need to occasionally fully discharge and recharge to erase “battery memory.” This couldn’t be more wrong for lithium-ion batteries. It’s a leftover myth from lead-acid cells and is actually quite undesirable to charge your modern smartphone in this way.

“Partial charging is just fine for lithium-ion batteries and can actually have some positive benefits for cell longevity. To understand why, it’s important to appreciate how a battery charges. When closer to empty, Li-ion batteries draw in a constant current and operate at a lower voltage. This voltage gradually increases as the cell charges up, levelling off at around a 70 percent charge before the current begins to fall until the capacity is full.

“Importantly, operating at a low voltage is good for a battery’s lifespan, increasing the number of available charging cycles before you’ll start to see a major reduction in capacity. Using up just 20% of your battery between charges isn’t going to be practical for most people, but topping up when you’ve used about half will see a notable improvement in your battery life over the long term, especially if you avoid charging up to full each time too. The bottom line is that small regular top-ups are much better for Li-ion batteries than long full charge cycles.”

Robert also revealed that many people don’t use fast chargers correctly. He says: “Fast charging technologies are a contentious issue as the higher current and voltages can definitely lead to a hotter device while charging. Fast charging was never really envisioned for full cycle charging. It’s a fast way to top up your phone quickly to get it back in your hands. Leaving your phone to quickly charge up for 15 to 20 minutes won’t lead to major overheating problems, but I certainly don’t recommend using them for overnight charging.”

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Damaged lithium-ion batteries are at risk of catching fire in a process called thermal runaway. 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.

Incidents of thermal runaway are on the rise, especially on aircraft,

Lithium-ion battery fires on board planes are rarely publicised but a fire in a device could emit toxic smoke and potentially the battery may even explode, causing damage to the aircraft and putting lives at risk.

One way to tackle such incidents is to use an AvSax fire containment bag which can deal with fires in personal electronic devices and are now carried on aircraft operated by 65 airline companies across the world – including some of the biggest and best-known.

AvSax  – which won the Queen’s Award for Enterprise in 2018 - has been used 28 times to deal with emergencies since the start of 2017.

More than 13,000 AvSax are now carried on aircraft worldwide. Deployment is so effective that extremely expensive diversions to alternate airports are avoided.