Apple’s apology for throttling iPhone performance has put the spotlight on iPhone batteries. I have been trying to learn more about this phone component which I have never really paid much attention to. This post is my attempt to make sense of what I understood from different sources.
Anyway, I have always been puzzled about the right way to charge my phone. I recall religiously draining my battery completely once a month as I had read that otherwise, the battery would ‘forget’ its capacity. I stopped when a techie friend explained that lithium batteries don’t forget their capacity, and draining them to ‘empty’ actually reduces their life. Sometime later, I got to know that charging the battery overnight was bad for the phone. I couldn’t understand why but stopped this practice just in case the claim was true.
By this point, I was confused by the conflicting advice from different tech gurus on the best way to recharge your battery. I asked myself what was the worse case scenario if I got my charging practice wrong? The answer was that I would have to replace the battery.
There was a good possibility I was going to get my charging practice wrong so I figured I might as well reconcile myself to having to replace my battery, sooner or later. And if I wanted to get the most out of my battery, I should take advantage of its 100% capacity. Like if I was going to be outdoors, a fully charged battery would last longer.
That decision simplified my life. Whenever I was within reach of a charging point, I would charge my phone to 100%. Based on my past learnings, I avoided overnight charging and got myself a battery pack to prevent my phone from completely draining.
That was the battery regime my iPhone 6S Plus was subjected to in the last two years with me. Initially, it seemed to be a good strategy. I would go to bed at night with the phone fully charged and disconnected from power sources, and wake up in the morning to find the battery still at 100%. But two years later, the phone has begun draining a lot faster. It’s 5.30 pm and it’s at 50% though I haven’t really been using it much. I put it down to an aging battery.
During these two years, battery technology started getting a lot more attention because of the world’s disillusion with fossil fuels, and the focus on EVs (electric vehicles) like Tesla.
The EV people figured out charging the battery to its full capacity and discharging it to zero would both reduce battery life. In order to maximize battery life, EV batteries are set to alert users that a battery needs charging when it’s around 25%, and the charger automatically cuts off charging at 85%. I’m guessing this means EVs will show 25% as ‘empty’ and 85% as ‘full.’
Now if EVs are that paranoid about overcharging and undercharging, why not phones? Well, an EV battery is unlike a phone battery because longer uptime is less important than extending battery life in an EV, for the simple reason that the battery is a far more expensive component in an EV.
After a bit of looking around, I found a website called Battery University which seems to have been doing some serious research into batteries. It’s a bit techy with graphs and numbers, but let me sum up what I was able to understand.
Basically, a battery is stressed and loses its power capacity due to two factors. The first is heat. If you keep your a battery in a hot environment, it’s going to deteriorate quicker. The second factor is keeping the battery at a full charge.
I had been wrong about my phone battery strategy, again. Not that I was surprised as Murphy’s Law has always applied to me.
Sorry, I’m going into ‘nerd mode’ as my curiosity has been aroused.
My charging cycle was whatever-discharge to 100%. According to the Battery University, that will cause my battery’s capacity to drop to 48% after a while (14000 charging cycles, to be precise). If I had stuck with a 25%–75% charging cycle, my battery capacity would only reduce to 74% for the same period. Increasing the charging to a 25%–85% cycle would cause the capacity to drop to 64% in the same time frame.
In short, if I want my battery to last longer, I shouldn’t charge it above 75%, and not let it discharge below 25%. Of course, the compromise is I will have to learn to live with less capacity (uptime) than a 100% charged battery.
I’m not sure I can live with that compromise. I mean what’s the point in having a phone if the battery is not going to last all day? The alternative is to charge the battery to 100% and just replace the thing when it deteriorates.
First things, first. Is my phone being throttled?
Google came to my rescue. Geekbench, the site that had discovered the throttling issue, has a $0.99 app called Geekbench 4. I downloaded it and ran a benchmark test on it, and then compared it with actual benchmarks for my phone model. From what I have heard, the Plus models have not been affected by throttling. The Geekbench test confirmed my phone wasn’t being throttled. My phone got a score of 2368 as against the model benchmark of 2400.
All those 99 cent app downloads of Geekbench must be adding up but I guess Geekbench deserves it. However, you can also check for throttling via a free app called Lirum Device Info Lite. You have to click on ‘This Device’ and then on CPU. As you can see below, the CPU actual clock and the CPU Maximum clock are the same on my phone, which means it hasn’t been throttled.
Lirum also does give some info about my battery. The battery wear level is 90% as full charge only goes up to 2500mAh as against the original 2750 mAh.
To double check, I downloaded a free app called Battery Life (be warned: there are ads at the bottom). It confirmed my phone battery’s capacity is down by 8%, which is not too bad after two years of use. This means at full charge my battery will give me 92% of the original 2725mAh. The thing is a few moments later, the app showed that the wear is 12%, which is average. It does indeed look like the system demands are causing my older battery to behave inconsistently. See below.
The Battery Life app didn’t give me details on how many charging cycles my phone had done. Google led me to a Mac app called CoconutBattery, which checks my phone from my Mac. Here are the test results on my 2-year old iPhone 6S Plus, a 5-year old iPhone 4, and a 6-year old iPad 3.
The present full charge capacity of my iPhone 6S Plus is 90% (2467mAh) and matches with the Battery Life app. It says my phone has completed 405 cycles of charging. This is guesswork, but I think my habit of constantly topping my battery charge might mean my phone has completed fewer full charging cycles. Not that it did the phone any good. The constant 100% charge seems to have stressed my battery, which may have been partly responsible for its capacity falling to 90% in just two years. In comparison, the 5-year old iPhone 4 is still at 85% capacity, while the 6-year old iPad 3 is at 83% capacity.
Windows users can use a trial version of an app called iBackupBot. It isn’t as slick as CoconutBattery but it seems to work. You install the app on your Mac (PC app is on the same page), click on your phone under ‘Devices,’ and click on ‘More Information’ in the right column. See red arrows on the left.
Out of curiosity, I ran some of the tests on my wife’s iPhone SE, which is less than six months old. She charges it to 100% and often forgets to recharge it till it shuts down. Geekbench says the phone isn’t being throttled and is actually running faster at 2559 than the model benchmark of 2410. Coconutbattery says the phone has had 52 charging cycles, and the battery is at 95.6% while Lirum rates the battery at 98% health. Interesting.
My iPhone isn’t being throttled at the moment. I did notice that my battery capacity reduces when the phone is hot. You can see the battery capacity actually increasing as the temperature falls from 1552 mAh at 31.6C, to 1554 at 30C, and then again to 1555 mAh at 29.7C. See below.
Keeping the phone cool does seem to extend battery life, and the phone does get hot when charged to 100%.
The wear level of my phone’s battery varies between 8% and 12%. That does not seem to be much. But the inconsistency is worrying as it indicates the battery could suddenly drain due to system demands, and the phone could abruptly shut down. This is precisely why Apple throttled iPhones with old batteries. It would seem my phone’s battery is a prime candidate for Apple’s $29 replacement program.
There are no Apple Stores in India so I called my local Apple dealer. He said that my phone has to be checked to see if every hardware component is in working condition. If all is well, they will replace the battery at a cost of ₹2250 ($36). The whole process will take 4–5 days. I may take up the offer.
One last thing
I have been having second thoughts about the 75%-25% charging cycle. I started out thinking I couldn’t compromise on using the full capacity of my battery. Later it struck me that I have access to a charging point or a battery pack at all times, and rarely use the 100% capacity of my battery.
I think I will stop charging my battery to 100% so as to extend its life.
Update: I was passing by my Apple dealer (a couple of weeks after writing the above post), and dropped in to have them check my phone.
The lady at the service counter connected my phone to Apple online and ran a free check, after which she announced that its battery had only run 410 charging cycles so it’s fine. My CoconutBattery app had said 405 cycles two weeks ago so Apple wasn’t really telling me anything I didn’t know.
I asked about the discounted battery replacement scheme, and she informed me that my phone was eligible for the scheme. However since the scheme is available for the whole year, she recommended I do the battery change in November.
It seems Apple recommends you change the battery only after 1000 cycles, and by November I would still only cross 600 cycles but get the most out of my present battery. She said the cost is ₹2000 or $32 (probably 10–12% tax on top). If the phone survives till November, I may do as she says as it should give my phone a fresh lease of life.
I say ‘may’ because tech is evolving at lightning speed so it’s pointless to plan that far ahead.