When Should You Charge Your Smartphone?

There’s a lot of public opinion about the best way to charge your smartphone. Most people take the easy route and simply plug it in while they sleep, letting it charge to 100% overnight. But is this the absolute optimal way to charge your phone? It may come as a surprise, but there exists an even better way to manage your battery for maximum lifespan.

What’s Inside the Phone?


To better understand how to treat a phone’s battery, we first have to look at what the battery is made of. If you’re using at least a semi-modern phone, you’ll find that it’s using a battery that’s based on lithium-ion. This is a very popular choice of smartphone battery these days and finds itself in a vast amount of units.

Lithium-ion batteries, unfortunately, don’t last forever. As it’s charged and discharged, it will begin to age and wear down. This is represented by the battery not holding its charge as well as it used to. You may have noticed this on an old smartphone; perhaps it used to go all day without charging, but these days, it goes flat in half the time. The time between removing the charger and plugging it in is called a “cycle,” and batteries may come with a cycle life expectancy.

So how do lithium-ion batteries respond to being charged in different ways?

Charging Methods

Thankfully, the people over at Battery University did a report on lithium-ion batteries. They looked at a study where lithium-ion batteries were charged and discharged at different charge ranges. This range is called the “state-of-charge,” or “SoC.” They then monitored how much the battery’s ability to hold a charge wore down as the battery underwent several hundred cycles. You can see the graph of results as figure 6 on their report.

From the graph, we can see that the absolute best way to keep your battery healthy is by charging it to 75%, then discharging down to 65%. Unfortunately, this is not a realistic expectation for a smartphone battery! It won’t be much of a “mobile phone” if you need to plug it in after a measly 10% discharge.

Thankfully, the second-best result is much more manageable; 75% to 45%. Batteries charged within this range kept just under 90% of their original charge retention after 6500 cycles. That’s a lot of charging!

By looking at the third best result, we can see that 75%-25% is the next optimal range. 85%-25% is the fourth best, albeit quite a way away from third. From this, we can see that lithium-ion batteries (when charged under realistic conditions for a smartphone) like to be charged up to around 75%, with 80% being a fine hard limit. This becomes more evident when you note that the bottom three performing lifespans all charged the battery to a full 100%. For discharging, it’s best to begin charging at around 50%, but 40% seems like a fine limit to go to if you need the extra lifespan.

But What About Battery Memory?


If you used early models of mobile phones, all this advice may fly in the face of the wisdom you’ve learnt. Perhaps you read the manuals for those phones and saw the dire warnings to always charge it to maximum when it’s first out of the box as well as fully discharging it before charging again. If you didn’t, you ended up shortening the battery’s lifespan. This was referred to as “battery memory.”

If you’re still in this camp, fear no more! The battery memory effect occurred back when mobile phones used nickel-cadmium and nickel-metal-hydride batteries. With the newer lithium-ion batteries being the norm, memory is no longer a thing, meaning you can do partial charges without damaging the battery. In fact, as shown above, the real killer is not partially charging them!

What Happens If I Fully Charge?


This is all well and good, but for some people, charging to around 80% and stopping is unrealistic. Perhaps the only charge time available to them is while they’re asleep, and nobody wants to wake themselves up in the middle of the night just to unplug a phone!

If you want to charge to 100% every time, your battery won’t explode or suddenly die on you. All it will do is cause more strain on the battery and cause it to wear down faster. Whether or not you want to go through the fuss of micromanaging the battery for a little more longevity is up to you. If you really want to charge to 100%, try recharging the phone when it reaches the 50% mark. Out of all the SoC ranges that charged to 100%, the one that recharged at 50% gave the best results.

Charging Forward

With lithium-ion batteries being the prevalent choice for smartphones, it’s a good idea to learn how to charge them best. After all, taking proper care of your battery will ensure a longer lifespan! Keeping a phone between 80% and 40% seems to be the best way to keep the battery healthy without sacrificing the ability to keep your smartphone mobile.

How important is battery health to you? Are you concerned for its longevity? Let us know below!

Simon Batt
Simon Batt

Simon Batt is a Computer Science graduate with a passion for cybersecurity.

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