Fast charging could be slowly killing your battery

Qualcomm QuickCharge 3
Qualcomm QuickCharge 3 (Image credit: Jerry Hildenbrand / Android Central)

Everyone hates the fact that we have to charge our phones. While smartphone battery life is getting better each and every year, we still wish there were some sort of fission reactor or something inside our phones so they would never need to be plugged in. That's why we love to hear about how fast a new phone can charge; it means less time plugged into the wall.

But like everything that looks good on the surface, there are drawbacks. With fast charging, those drawbacks could be pretty serious when it comes to battery health.

Battery health: What is it?

OnePlus Warp Charge charger

Source: Andrew Martonik / Android Central (Image credit: Source: Andrew Martonik / Android Central)

In case you're not sure what that means, battery health is a term that describes how much a battery has degraded since it was brand new. Battery degradation means that the actual capacity is diminished and that means two things: you spend more time on the charger and you eventually have a phone that won't take a charge at all.

A battery starts degrading the moment it is first charged. It's convenient to measure battery health in charging cycles, but every time you apply voltage to charge a battery it is shortening its life. You've probably seen this in action and had a phone that didn't seem to stay charged as long as it used to after a year or so, and every single rechargeable battery has this issue. It's not a problem, it's just how the science works.

Your phone's battery health degrades from the moment it is first charged.

I'm not going to get into the minute details about how batteries charge. It's sufficient to know that to create a charge inside a battery you have to remove a very thin layer of material from an electrode inside of it and transfer that material to another electrode and the surrounding fluid known as an electrolyte. The same happens when you discharge, only in reverse.

As these materials degrade over time, so does the life of your battery and the actual capacity lessens. Eventually, you start to notice that you used to be able to go 15 hours on a full charge but now you only get 11 hours, for example. That's because your battery isn't storing as much as it used to.

It's not a bug, this is just how it works.

This is a function of a rechargeable battery and not a bug. It happens to the batteries in our phones, the batteries in PlayStation controllers, even the batteries in an electric golf cart. When chemistry meets physics you realize there is no perpetual engine. And one factor makes the whole process much worse: heat.

Battery health: Why you should care

Samsung 45w Fast Charger

Source: Ara Wagoner / Android Central (Image credit: Source: Ara Wagoner / Android Central)

You can not escape the heat when dealing with a battery, especially one that's designed to be recharged. Using a battery makes it get hot, charging a battery makes it get hot, and even leaving a battery alone and doing nothing with it can make it get hot. You're dealing with very acidic compounds and volatile metals and the two can produce a very strong reaction. That means the most important thing to prolonging battery health is reducing the heat.

To prolong battery health and life, you need to beat the heat.

While I'm not suggesting that we charge our phones inside the freezer, we do need to understand how fast charging tries to balance reduced time on a charger versus long-term battery health, especially now that we've been told that 125-watt charging is coming and it takes just five minutes to charge a battery to almost half of its capacity. Yikes.

Oppo didn't give away all the secret science behind its 125-watt Flash Charge technology but it did mention one thing that's a bit concerning — the system is designed to keep the battery temperatures below 40-degrees C (104-degrees F). The company does mention a change in battery type from 3C to 6C, but traditionally that designator has been used to measure power discharge, not thermal protection.

Ideally, a manufacturer would want to keep the battery temperature below 30 to 35 degrees because it knows how heat can destroy a battery's usefulness. I'm not here to second guess the engineers at Oppo because they are clearly really good at what they do. But I worry that manufacturers are becoming more concerned about fast charging than longevity because they think that's what we really want.

125-watt charging at 40-degrees C is crazy to think about.

I can't speak for everyone, but I don't want a phone that charges X% faster but I notice the battery going bad in 18 months. That's a real concern when the time spent charging is accompanied by temperatures that are higher and higher than ever before. It would be different if batteries were easy to replace and didn't require a heat gun, new gasket materials and adhesive, and a whole lot of luck to get to them.

I'm picking on Oppo here because it just announced some crazy-fast new battery charging tech, but this applies across the board. Fast USB-C PD charging is bad for batteries. Qualcomm Quick Charge is bad for batteries. So are Warp Charge and every other turbo-powered name given to the technology that charges batteries using more voltage, higher amperage, and more heat.

Like you, I hate having to charge my phone. But I hate the idea of having a phone that's only a year and a half old with a busted battery a lot more. I hope battery technology that allows for these higher temperatures is evolving at the same pace that charging them faster is.

Jerry Hildenbrand
Senior Editor — Google Ecosystem

Jerry is an amateur woodworker and struggling shade tree mechanic. There's nothing he can't take apart, but many things he can't reassemble. You'll find him writing and speaking his loud opinion on Android Central and occasionally on Twitter.

  • If I could charge the entire battery in under 30 minutes, why would I care if it doesn't last 15 hours? I've had Samsung phones for years now, and never a model outside the Galaxy S5 that had a replaceable battery, but the life on this phone (currently using the S10+) seems relatively close to what it was when I bought it. It gets hot and is on a fast charger or wireless fast charger all the time. Just the price you pay to carry around a computer in your pocket.
  • Because if it lasts 8 hours, you are going to be charging it twice a day, effectively cutting your battery life in half.
  • I've literally been saying this regarding iPhones. It's also directly related to CLOCK SPEEDS for CPUs which is also how computers work. Somehow though we as society are ignoring this and allowing Apple to be sued for using software controls over an operating systems task management. Does anyone have any idea how many things are prevented from running in a windows OS?
  • If anyone is intrigued or concerned about this topic, I can save you a lot of worry and just use your phone. For every study that shows this or that behaviour somehow destroys your battery faster than others, you can find another contradicting it. Just use your phone. If you find it more convenient to charge nightly on a fast charger overnight despite being at 75%, do it. If for some reason it's more convenient to leave it plugged into a slow charger during the afternoon while you use it at your desk, do it. If your battery starts to die after 2 1/2 years, replace it. There are so many more important things to worry about and the battery tech out there right now is pretty good.
  • Jerry has been promoting fast charging instead of decent battery life for years. Finally an acknowledgement that it has issues.
    @JClforsure - have you seen the cost of battery replacement? And have you seen the manufacture date of replacement batteries - pretty much from the phone's release, as they are all oem and there is negligible alternative supply. Overnight does not need fast charging. In fact, it is only necessary if you use your (small battery) phone away from charging facilities, but briefly are near power points. Why you'd want to carry the dedicated charger, or have one in each place you might charge, is beyond me.
    Since I got a phone with a decent battery I've had no worries about the phone dying during the day, and no need to carry an external power pack. A slow overnight charge from around 25% has been more than enough to last a busy day.
  • I have my phone mounted on the air vent and drive all day and use my phone all day for uber. And my car gets hot even with AC. Would that affect my battery? Even it charging mounted on the vent
  • You can use the Accubattery app to see what the temperature of your phone is while you charge it. You can also use it to monitor your overall battery health.
  • What is the battery monitoring app you show in the main picture?
  • It's a battery overlook app called Ampere
  • Thank You rave_97
  • Wouldnt be an issue with removable batteries. With that being said, for the $30 or whatever it costs for a replacement battery, I'm not that worried about it. Fast charge all the things. 
  • It's not usually the cost of the battery itself that is balked at. It's about $100 to get it replaced for an iPhone. Yea, some can do it themselves, but that is no where near the majority.
  • Not even close to $100... Not to mention apple was running the $29 special for a battery change a few months back. 
  • I've had half a dozen iPhone batteries replaced at a local authorized shop. Most are $30 or a bit more. My 6S Plus was $40. I change my Android batteries myself, and they range from $11 to $24. You have to watch out for cheaper batteries because they have a resistor instead of a real temperature sensor on the charge controller. My wife's old M8 battery is always 87 degrees F, lol.
  • Everyone is so concerned with an all metal or metal and glass phone. My wife and I have OnePlus 8s and since we put cases on them anyway, we'd both rather have removable batteries for various reasons. People always prioritize the wrong things. Stay healthy!
  • It is because sites like this cried "boo hoo, plastic" and they want "premium" (although not sure how a glass and metal sandwich is "premium") so the manufacturers started moving away from those materials. I miss the days of removable batteries and not having to worry that every little drop might cause it to shatter into pieces.
  • I still have a handful of old LG batteries from my swapping days. I don't miss it. I get two days of battery life regularly, and can do 5 if I'm careful. At least in my opinion, that's better than carrying spare batteries to make it through the day. My family has busted 14 iPhone screens, and those were the ones with plastic and metal bodies. My U12+ has been dropped onto a granite floor (I missed my shirt pocket!), and bounced with no damage. It's also been dropped onto an iron table foot, and slammed onto carpeted concert with over 200 pounds of force behind it. Yes, I'm fortunate, but not every phone is made equal. The screen has a metal ring embedded in the edge that dissipates force (looks cool too), and the glass back is actually flexible. In contrast, my Galaxy S7 Edge shattered instantly on the first drop.
  • Meanwhile, in some review somewhere, Sony is criticized for having ONLY 18W fast charging.
  • Yes, you know that's going to happen.
  • I have been saying this for years. I use a 2.5W (500mA) charger overnight. 6hrs=15Whr approx 4000mAh I only use fast chargers when down around 30%. Then the battery is "thirsty" enough to handle the high power feed.
  • Excellent article Jerry. I've felt the same way for years. I will always charge as slow as possible because it generates pretty much no heat. If I'm in a time crunch I will use the faster stock charger but it's not often. I did notice you mentioned the new 125w charging at 104F. Oddly enough, that's actually lower than my stock 3a 18w charger which sits at 109F during peak charging. I feel like this is way too hot and is why I don't often use it.
  • I do similar. I deliberately don't use the charger that came with my S10 when I go to bed because it's going to be there long enough anyway. I use this in another room when I need fast charging.
  • I'm confused, Jerry.
    You only need the battery to last 12 months, not 18+
  • I bought the Note 8 three years ago. No good reasons to upgrade yet... Battery is fine. Only sheep upgrade annually.... Dumb sheep. I've owned cell phones for over 25 years... The smart stuff sold these days does not need to be upgraded often. Lmao, would you upgrade a PC annually? Of course not.
  • We should be expecting batteries to last longer than 1 year. 2 year phone contracts are the norm, it's unnecessary to change a phone that's less than 3 years old and climate change is real.
  • Dash charging on OnePlus (and OPPO phones) work differently than Qualcomm's quick charge. The draw back is you have to use their proprietary charger but this is well worth it for the following reasons. Dash charge puts all the voltage regulators that protect the battery in the charger instead of in the phone (like QC Quick Charge does) so the charger brick gets warm, not the phone. They also use higher current instead of higher voltage to charge faster which keeps the temps down thus eliminating the heat issue that degrades batteries. I've also found that with Dash Charge, I just charge while I drive to work every morning. That gets me to around 80% which is more than enough to get me through the day until I drive home where I can top it back up to 80% if I need to. I rarely need to.
  • Some of what you said is accurate. Higher volts can run cooler as it would use less amperage but still the same power. Resistance matters.
    however vooc uses 5v4a to match battery voltage, more pins (less syyem resistance) , and reduce regulators in the phone. The newer stuff starts using dual cells different charge and discharge paths, etc. Those batteries are going to be super expensive and proprietary just like the dash bricks. At some point is gets pointless. Do you really need to charge your phone at 125 w if the battery last all day?
  • Fully agree with your last point. There is no reason for a 125w charger for people who plug in then go to bed. Other chargers are plenty fast enough to give you a top off in 15-20 minutes to finish your day. My charging habits have definitely changed with fast charging. Sitting here at 5:00pm with 51% charge. I'll likely charge tomorrow while I drive to the trailhead.
  • Keeping the battery temperature below 86 to 95 degrees Fahrenheit is not gonna happen. The phone will be in your pocket or in your hand picking up body heat, so the normal temperature is going to be near 100 degrees F during use, and up to 115 degrees F when gaming. Also, I would not lump all charging methods together. QC 2.0 generates lots of heat, QC 3 generates less, and QC 4 and 4+ leave the phone cool to the touch. USB PD is not as cool as QC 4+, but it was better than QC 3 in my tests. Me? I use a normal charge rate power bank that turns off when the phone gets full, but if I wait until morning and need it faster, I use USB PD. I do have the advantage of not needing to charge every day, but that is offset by hardcore gaming and lots of camera use. You know what has it really bad though? Wireless charging. Heat from the induction process, plus heat from the battery controller, plus heat from the battery being charged itself. So, Jerry, will Android Central continue to promote fast charging and wireless charging?
  • I charge wirelessly every night and the phone doesn't increase in temperature at all. Do a slow charge over night and it's fine.
  • I should have mentioned I was referring to wireless fast charging. My bad!
    Out of curiosity, have you checked your battery temperature after it's been on the charger for a bit below 50%? I'm kinda interested in what it is for slow wireless charging.
  • Worst case is $60 to get an iPhone battery out of warranty. That is not crazy expensive. Breaking the glass back, that is.
  • Totally agreed. This is just like when manufacturers all thought we wanted thinner and thinner phones without ever consulting anyone. I find the S10 18w (think?) is decent. I cannot imagine I'd need more than the 25-30w we have now. Batteries warping is a real thing and heat caused this, even if by this point it maybe a few years old. On my S7 it caused the back of the case to bend as the battery expanded.
  • I've never fast charged a phone. I'd be surprised if I do 8n the next few years.
  • For years I’ve actually intentionally purchased a slow charger for my bedroom. Overnight, I charge as slowly as ideal since I don’t need it for (ideally) 8hr, but then I’ll place the out of the box fast charger in my living room for the rare occasion I’ll need to top the device up mid-day.
  • I miss having replaceable batteries, like my old Palm Pre.