Is Fast Charging Bad For Smartphones? – Science Explained!

The fast-charging technology world is touching higher and higher level every day. Earlier, a smartphone used to charge at 5W, but now we have touched 120W milestones.

Yes, I’m talking about Xiaomi HyperCharge and Vivo SuperVOOC 120W power bricks that fully charges a 5000mAh battery in less than 20 minutes.

But an obvious question everyone asks- is fast charging bad for smartphone battery health?

Fast charging is totally safe as long as you’re using the original charger and cable. Smartphone brands like Xiaomi, Oppo, Realme, etc., use battery protection circuits in the adapter that controls the charging speed smartly.

The adapter supplies maximum current when your battery is totally drained and reduces the current output once it reaches 80%. Hence, it prevents your smartphone from overheating.

If you’re also worried about your smartphone battery health because you’re using a fast charger, this guide will be helpful for you.

What is Fast Charging?

Fast Charging

Let’s understand what is fast charging. Because it’s a common term that every smartphone brands are using as marketing gimmick.

A typical normal chargers comes at 5W which delivers 1 Amp DC current at 5 volts. This 5W adapter takes more than 3 to 3.5 hours to charge a smartphone battery from 0 to 100.

5W adapter is the market standard and anything more than 10W can be presented as fast charging. But nowadays, all flagships comes with 15W power brick out of the box.

There is no market standardization on fast charging but higher the wattage charges your device quickly.

Apple’s 20W adapter takes approx 1 hour to charge an iPhone 13 Pro battery. So, it’s definitely a fast charger in comparison to older 5W adapter.

But, Xiaomi 120W HyperCharge only takes 17 minutes to charge the Xiaomi 11T smartphone. It’s also a fast charger but we can’t say 20W is slow charger.

Does Fast Charging Ruin Your Battery Health?

Fast Charging 120W
Image Credit: GSMArean

Fast charging doesn’t ruin your battery health quickly because phone manufacturers divide the charging speed into two segments.

When your smartphone battery is completely drained, the chargers push maximum power to juice up the battery fast.

Once your battery recharges to 80% or 90%, the charging speed is decreased to prevent overheating.

You must have noticed this with your smartphone. Your phone charges very quickly from 0 to 80, and then it takes more time to reach 100.

Also Read: Does Using Non-Apple Charger Ruin Battery Health

How Do Phone Companies Mitigate The Impact Of Fast Charging?

Higher wattage increases the chance of overheating which ultimately impact the battery health because lithium-ions loses it’s power holding capacity at higher temperature.

So, how does smartphone companies mitigate the impact of fast charging on battery health?

Here are two techniques are used by phone manufacturers to reduce the impact of fast charging-

1. Dual Phase Charging

Have you seen this claim by smartphone manufacturers – ‘this phone will charge 0 to 50 in just 5 minutes or 0 to 80 in just 10 minutes“.

They are using dual phase charging techniques to mitigate the impact of fast charging on battery health.

The phone or power brick has a dedicated power management circuit that smartly mange the charging speed.

When you phone battery is completely drained, your power brick delivers highest current to juice up the battery immediately.

In this phase, lithium-ions quickly gains the power without overheating. Once the phone recharges 50% or 80%, power brick reduces the current to mitigates the scope of overheating.

2. Dual Battery Design

In this method, a 5000mAh battery is divided into two 2500mAh batteries. Now, the power adapter delivers same power to both batteries which reduces the charging time by half.

But, this method makes the phone bulky because size of two 2500mAh batteries are more than a 5000mAh battery.

Also Read: Can You Charge AirPods With a 20W Charger

How To Slow Down Battery Aging?

Typically an smartphone battery is designed for 800 charge cycles. Which means if you charges your smartphone once a day, it will last 2.5 years without any problem.

But, your charging style, uses, and other factors also affect the battery health.

If you’re concerned about your battery health, you should follow these tips to slow down your battery aging.

1- Avoid High Temperatures

Lithium-ion cells uses an electrolyte gel that is permeable to Li-ion flow but impermeable to electron flow. If the temperature around the Li-ion battery is too low or too high, the electrolyte forms SEI layer around the lithium. [study]

This layer reduces the charge holding capacity of Li-ion batteries. So, if you want slow battery aging, then avoid using your smartphone near too high or too low temperature.

2- Don’t Drain Battery To Zero

If you don’t want your phone battery to loose it’s power holding capacity, never drain the battery to zero.

Lithium-ion batteries never likes to be fully discharged. So, connect your charger once battery drops below 20%.

3- Avoid Full Charging

Never fully charge your smartphone battery if you want longer lifespan. Lithium-ion batteries goes under higher strain when they’re fully charged.

Apple also recommends ideal charging range is between 20 to 80 percent. To extend the battery lifespan, Apple introduced Optimised Battery Charging in iOS and macOS which stops your device from charging beyond 80.

4- Remove The Case While Charging

Most smartphone users put an armoured case on the phone to protect against accidental damage.

But, these cases are not a good conductor of heat and when you fast charging your phone, you protective case will trap the heat which is not good for Li-ion batteries.

So, it’s better to remove your smartphone case while charging. If you’re not using a super fast chargers, there is no need to remove the case.

5- Use Certified Charger and Cable

Some smartphone companies puts battery protection integrated circuits in their charging brick to control the charging speed.

If you’re not non-certified third-party charger, it won’t control the current rating as per your phone requirements.

As a result, your battery will age fast and lose it’s capacity. So, it’s recommended to use original charger and cable.


Fast charging will not affect your smartphone battery health as long as you’re using the original charger and cable.

Generally, the charging speed is reduced when your battery recharges 80%. That’s why you have noticed that your phone charges fast to a certain limit and then speed drops.

About Daniel

Daniel is a tech enthusiast and repair technician who loves experimenting with various gadgets and home appliances. On this blog, he shares a troubleshooting guide for software and hardware faults.

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