Some people just plug their phone into a charger (or toss it on a wireless charging pad) whenever power is available. Others fastidiously keep their battery between 40% and 80%, never allowing a full charge, under the belief that the battery will last longer as a result. Personally, I keep my iPhone on a Qi wireless charger on my desk all day while I’m at work, and I juice it up overnight, as well.
Charging your battery causes its performance to degrade over time, no matter how you do it. Smartphones are powered by lithium-ion batteries, which work by moving charge carriers (in this case, lithium ions) from one electrode to another. The ions move in one direction when charging and the other when discharging.
Charging your battery to full capacity less often, and not letting it run totally dry, can extend its life—somewhat. Putting less stress on the electrodes results in less degradation, and ultimately higher capacity for a longer period of time. “It is possible to prolong the battery life by not completely charging and not completely discharging. So we’ll say stay between 20% and 80% or so,” de Vries told us. The battery lifetime is “inversely proportional to the amount of lithium ions that you put in the electrodes.”
Heat is another factor that negatively affects battery life. “Heat is the worst enemy of batteries,” according to Battery University, a repository of battery science information maintained by battery-testing company Cadex. “Lithium-ion performs well at elevated temperatures but prolonged exposure to heat reduces longevity.”
What the manufacturers say
The major phone manufacturers declined to provide any recommendations for specific charging techniques when we asked, but they do offer vague tips on their websites.
Apple says that you should “charge your Apple lithium-ion battery whenever you want” and goes on to advise that “there’s no need to let it discharge 100% before recharging.” On a different page the company notes that you should avoid extreme temperatures (especially over 95 degrees Fahrenheit) and remove cases that might cause your iPhone to overheat while it’s charging, but Apple doesn’t state when you should or shouldn’t charge or suggest any optimal charging thresholds.
Google’s recommendation is similarly straightforward: “Charge as much or as little as needed. You don’t need to teach your phone how much capacity the battery has by going from full to zero, or zero to full, charge.”
Samsung advises charging regularly and keeping the battery above 50%. The company also states that leaving your phone connected while it’s fully charged may lower the battery life.
Even if constant charging affects battery life, will you ever notice?
So, charging your phone all the time and letting it run dry are habits that could shorten its battery life. But are they liable to have enough of an effect to make a practical difference before you upgrade to a new model?
If you don’t upgrade regularly and don’t follow ideal charging practices, it stands to reason that you may find your phone’s battery life lacking over time. However, other factors—such as how much you use your phone in general—likely have a much larger impact on battery longevity than charging behavior. That’s because lithium-ion batteries are rated for a specific number of charge cycles, or times they can be filled up. (These cycles are cumulative, so two charges from 50% to 100% count as one cycle.) So the more you use your phone, the more you have to recharge the battery, and the more it degrades.
A loss of 15% of your battery capacity over two years is noticeable, sure, but it leaves enough juice—especially with the larger batteries in newer iPhone models—that most people can still get through the day without plugging in. For heavier phone users who wear down their batteries quicker, or those who have older phones with smaller batteries and more marginal battery life to start with, the good news is that batteries can be replaced fairly cheaply. Apple charges $50 or $70, including labor, depending on your iPhone model. Best Buy will replace a Samsung Galaxy battery for $50. uBreakiFix, Google’s walk-in repair partner for Pixel devices, charges about $80 to $110 to replace batteries. Or you can do it yourself, by following the guides on iFixit.
Ultimately, it’s a matter of convenience
In the long run, you need to choose what’s right for you: babying your battery to extend its life, or charging it at your convenience so that your phone is more likely to be juiced up when you need it.
“It would be better for a phone battery to be allowed to gradually lose its charge, then recharge when needed, perhaps to 80%, before stopping again,” said Purdy. “Of course, some people don’t want to risk having their phone keep only a partial charge before they head out. Or have a part-time job watching their battery percentage.”
de Vries echoed that thought. “If you charge the battery only half way, okay, it will last longer, but it will be empty sooner than if the battery has been fully charged. So it is a trade off between the total life of the battery and the amount of times that you have to recharge it.” He told us that even though he is intimately familiar with optimal battery hygiene, he doesn’t always practice it. “I’m lazy,” he said. “Back in the old days, I’d look every quarter or half hour to see if my cell phone, my laptop was charged already. And then I would stop, for instance at 90%, 95%. But sometimes you forget.”