Why does charging a phone battery to 100% keep the discharge rate slower than charging to 90 or 80%?


I have experienced it on multiple mobile phones and my laptop. If i charge the battery to 100% the discharge to 99% is way slower than if i charge the battery to 90% and discharge to 89%. And this makes me charge the battery to 100% even when I know that it is bad for the battery just because the charge lasts much longer than charging to 90 or 80%. Is it related to some kind of chemistry?

I am ok with eli 20 also. Thanks.

In: 2

6 Answers

Anonymous 0 Comments

My understanding is that when you charge to 100%, it is really ~90% (for example), which is the “safe spot” you are thinking of. Thus if you charge up to 100% for a little longer, you really get closer to “100”. And then as you use battery life and it starts to drain, it isn’t really registered as falling until you get down to the point where the software was telling that you were at 100. So effectively, it is not a linear sliding scale yet. By contrast, if you stopped charging at 80 or 90%, say, then you are already in the linear sliding scale, and you see the delta in % immediately.

Similar to how old cars’ gas tank gauges behave. You fill the car up beyond the 100% point, and fuel starts to fill the path to where the cap is screwed on, then as that gas is consumed, the car still sits at 100% Full. The gauge starts to move after you settle into consuming what’s in the actual tank.

I think.

Anonymous 0 Comments

Charging it all the way to 100 and draining it to 0 puts a lot of stress.on the battery. Keeping it between 80 and 20 is a lot less stress. It’s like bending a paper clip back and forth, the more you do it, it eventually breaks. If we don’t bend it as far, it’s less stress, and the stress is highest at the extremes.

Anonymous 0 Comments

Cell phones, laptops and tablets are all made where the battery percentage indicator isn’t a true indicator of how much battery is there. They intentionally make it look like it is discharging slower when it is full, so you think you are getting great battery life. There is no laws that say the battery percentage had to be an accurate representation, so it is really whatever the manufacturer wants it to be. This is also why is discharges so much faster below 50%. Also, for all of them, when the battery says 0%, they aren’t actually empty either.

Anonymous 0 Comments

A battery puts out fewer volts as it is depleted, so in order to get the same amount of energy, the amperage used must increase (watts = amps x volts)

Battery capacity is measured in amp hours (or really milliamp hours) so if you’re using amps at a faster rate, the percent remaining drops faster.

Anonymous 0 Comments

It’s not necessarily intentional, but measuring battery capacity/charge is not easy.

Typically you do it by measuring the voltage over the terminals, but that will also change depending on how much load is out on the battery (i.e. it’s high when the battery is not being used, drops when the phone pulls a lot of current).

Modern smartphones are a little more sophisticated, they might use impedance testing, voltage testing, a coulomb counter that records how much power has been used and also some algorithms that adapt these calculations to the battery’s behaviour over time.

All that’s to say, it’s not an exact process and things can be slightly wrong all the time.

Anonymous 0 Comments

There is actually a lot to this question and kind of need to explain several things like measuring battery charge, battery health, and good old ohms law. But essentially, at full charge your battery is able to put out its full voltage, however this voltage drops during discharge. As voltage drops, current (amperes) must be increased which In turn uses more battery faster.

Now more importantly, stop fully charging your phone. You might think it’s better because you get a little bit more use time out of it but you’re screwing yourself over. Battery charge is estimated from how much voltage it’s giving out. Fully charging a lithium battery permanently damages the chemistry inside the battery and will impact the total voltage the battery can produce. It’s only a tiny amount each time, but it adds up eventually. Battery wear indicates the loss of maximum voltage the battery can produce, which means it needs to use more amperes to operate which in turn gives you less overall battery life.

The problem with phones then cascades. As newer and newer phones are made, they demand higher CPU power (voltage) to operate properly. If you have a phone that’s a year or two old and you haven’t treated the battery nicely, you will find that your phone struggles because the maximum voltage it can put out isn’t good enough to keep the CPU operating at a high frequency. People refer to this as phone manufacturers purposely bricking their phones with software updates to force them to upgrade. It’s not. It’s people misusing their phones and after that 1 – 2 year mark when battery wear becomes a problem, their phone starts sucking.

My current, and last two smart phones have always lasted me at least 5 years of great performance. I hate this idea of upgrading phones every plan cycle, it’s horrible for the environmental and completely unnecessary. You’re just feeling Apple money for no reason. I currently have a pixel 4 (and it’s still fast and I have zero issues with it), it’s exactly two years old at this point. I use an app to manage my battery and it currently reports my battery wear as 94%. This means in those two years I’ve only lost 6% of my battery capacity. I’d guess for people who charge their phones a lot they would have at least double that in two years, maybe more. The more you look after your battery, the longer your phone lasts