You’re charging your phone all wrong: 6 common myths, debunked

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ZDNET’s key takeaways

• Charging to 100% stresses your battery, as most cap at 80%.
• Certification matters more than brand when picking a charger.
• Draining to 0% doesn’t ‘calibrate’ a lithium-ion battery.

Not a week goes by that I’m not correcting someone who is still recycling some battery myth packaged as a “tip” from the nickel-cadmium era (also known as the 1990s). 

These tips have been repeated and regurgitated so many times. A quick Google search (or an AI prompt) turns up plenty of articles that reassure readers that the tips are 100% grounded in present-day, lithium-ion era reality, when they most definitely are not.

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I’ve picked six charging habits that people ask about constantly, and checked manufacturer documentation. When the manufacturers offer vague answers, I’ve referred to peer-reviewed battery research to get a definitive answer.

So, let’s lay some myths to rest, at least until the lithium-ion era gives way to whatever comes next.

1. You should always charge your phone to 100%

If there’s one thing that people seem to get super anxious about, it’s the charge level of their smartphone’s battery.

This situation is why manufacturers introduced charging mechanisms to halt charging once the battery got to 80%. Apple has Optimized Battery Charging, while Google has Limit to 80% on the Pixel.

Apple says that this feature “is designed to reduce the wear on your battery and improve its lifespan by reducing the time your iPhone spends fully charged.” Google says it added this feature “to prioritize the long-term health of your battery.”

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Samsung is even clearer, saying that “keeping your Samsung Galaxy charged to 100% may seem like the best way to maximize usage, but lithium-ion batteries naturally experience more stress when they remain at their highest charge level for extended periods.”

Verdict: False

2. You must run your battery down to 0% before recharging to ‘calibrate’ it

Seriously, stop doing this. This myth is a holdover from the 1980s and 1990s when rechargeable batteries used nickel-based chemistries, such as nickel-cadmium (NiCd) and nickel-metal hydride (NiMH). These batteries did suffer from a voltage-depression effect due to partial cycling, commonly called “memory effect.” Lithium-ion, which is what’s in every phone sold today, has never had that problem.

Google states it plainly: “You don’t need to teach your phone how much capacity the battery has by going from full to zero charge or zero to full charge.”

The same Google support document includes a section that says to keep the battery capacity data accurate for measuring battery wear, “your Pixel needs to fully charge at every 10th cycle.” This step is related to battery wear reporting, not to prevent battery wear.

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Battery University, a site that dives deep into all things battery-related, also says clearly: “If at all possible, avoid full discharges and charge the battery more often between uses.”

Verdict: False

3. Leaving your phone on the charger overnight overcharges and destroys your battery

I hear questions about this habit a lot, and clearly Samsung gets asked it a lot too, because the company has a page that addresses this question directly: “Absolutely not! Your phone’s battery will not be at risk of overcharging if you leave it plugged in overnight.”

Modern chargers and batteries are incredibly smart and resilient, and manufacturers have controls to prevent overcharging.

However, I have noticed that Samsung might be adding to the confusion, because an undated page on the official Samsung website advises owners to “unplug the charger after the device has reached a 100% charge to avoid a swollen battery.”

Verdict: False

4. It’s fine to charge while the phone is cold/hot as long as the charging icon is showing

There’s no quicker way to wreck a battery than to charge it when it’s too cold, or it’s too hot.

Battery University doesn’t pull any punches when it comes to sub-freezing conditions: “Many battery users are unaware that consumer-grade lithium-ion batteries cannot be charged below 0°C (32°F).” 

The battery will appear to charge normally, but inside, metallic lithium will coat the anode, permanently damaging the battery’s performance and safety.

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When it comes to heat, all three of the big manufacturers flag this issue as their main concern. What makes charging in hot conditions worse is that the act adds to the problem by generating even more heat.

What is good is that all three manufacturers specify the identical charging temperature window: 32° to 95°F (0° to 35°C).

Bottom line, don’t leave your phone charging somewhere like a car dashboard, in direct sun, or under a pillow, and if it seems to be getting hot when wireless charging, take the case off.

Verdict: False

5. Using your phone while it’s plugged in doesn’t affect the battery

OK, Samsung addresses this issue directly on a page titled ‘Can you safely use your Samsung Galaxy while charging?’

The answer is, “Yes, you can use your phone or tablet while charging.” The page explains that the only drawback to this approach is that the device will take longer to charge.

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However, going back to the previously mentioned undated charging tips page, Samsung has a caveat that I think is worth adding: “Browsing the web, watching a video, and playing games while your phone is charging will lead to a slower charging rate in order to prevent overheating.”

So, it’s OK to touch and use your phone while it’s plugged in, but be mindful of the extra heat that this technique can generate.

Verdict: True… but with a caveat

6. Use any USB-C charger as the expensive ones are a rip-off

Here’s what the manufacturers have to say about this habit:

• Samsung: “Always use an authentic Samsung charging cable and plug to avoid battery deterioration and damage. Always use a charger that fits. An incompatible charger could damage the USB port.”
• Google: “Use the power adapter that came with your phone. Other power adapters and chargers can charge slowly or not at all. They can also damage your phone or battery.”
• Apple: “You can also charge iPhone, iPad, Apple Watch, or iPod with ‘Made for iPhone’ or other third-party cables and power adapters that are compliant with applicable country regulations and international and regional safety standards. Or you can use a Mac USB-C Power Adapter. Other adapters might not meet applicable safety standards, and charging with such adapters could pose a risk of death or injury.”

Of all the answers, Apple’s is the best. The other two companies are hedging because they can’t guarantee anything beyond the charger they supply or sell, and their answers seem to suggest there’s some secret sauce in a Google- or Samsung-branded charger.

The problem isn’t what’s written on the charger, but what’s inside. A charger that doesn’t properly negotiate voltage and current, or one that delivers unregulated power or out-of-spec voltage, can push more heat into the battery. This is what can happen when you use a cheap, uncertified charger from an online seller.

Verdict: False… but with a caveat

The bottom line

There you go. You’re now armed with the best 2020s-grade information on how to charge your smartphone, not 1980s-era nonsense.