Even smart phones get confused

I've owned the Pixel 6 since it was released; just like the Pixel 1XL and Pixel 3XL I ordered it during the announcement, so I've owned it since October 2021. As of June 2024, my Pixel 6 battery life has been poor for the last 6-9 months but I just assumed the battery was slowly failing. What happens is that every day 4 or 5 hours after taking it off the charger the phone would show the battery to be 60% charged. I thought the battery was shot, however, one day it suddenly showed 3% about mid-afternoon when I had not charged it yet that day, and out of curiosity I just left it alone. It quickly went down to 1% but then stayed there for at least 10 hours before it shut off. That told me maybe Android's battery calibration is just incorrect.

Smartphones, tablets, computers, etc, keep a map of battery charge so they can give you a more accurate view of your battery status. Lithium Ion batteries change their voltage very little during the majority of their discharge so it's hard to say what to call a specific percent without mapping it. However, over time it can get calibrated incorrectly.

We can test that!

So to test this I charged the phone to 100% the next day and I just let it discharge over the day. I only used it lightly, but otherwise normal usage including the normal apps that sync, notifications, emails, etc. I also disabled Battery Saver so that it would discharge faster than the last 20%. Ultimately the phone ran 40 hours, which works out to an average of 2.5%/hr which is pretty typical in my experience when your phone is actively doing things (cellular, wifi, apps syncing, etc).

I charged it the next day and when I powered it on the battery had gotten so low the fingerprint reader lost data (so that was annoying) but then strangely when I recharged it, it only charged about 40 minutes on an 18W charger to 100%. According to various sources, this phone will charge from empty to full in about 2 hours, so it seems that the battery is either not being used to its full capacity or has lost capacity. Uh oh. I then again used it very lightly that day and 4 hours later the phone was showing the battery at 82% so I'm not sure if anything has improved. By the end of the day (15 hours or so) it was starting to look pretty good at 55%. Improvement!

The day I charged it normally and again used it lightly and at bedtime, the battery was in the 50% range.

I kept this pattern of usage for another week and it continues to be around 60% by bedtime so I'm convinced that the primary problem with my phone "running out of battery" by lunchtime was just calibration.

I've not played any games on the phone during this testing. I know games are pretty hard on the battery, so I plan to resume some normal gaming on the phone in a few days and then compare the results.

Two month update; battery life has seemed pretty okay since the re-calibration. I typically see 45-50% by bedtime now after normal usage of the phone during the day. Some days more, some days less, depending on how I've used the phone that day, but this is a vast improvement over seeing 60% at lunchtime.

Annoyingly, four or so months later this crept back in slowly and at five months I'm calibrating again. The phone was at 1% for 14 hours and the battery was still at 3.652V. I don't know the exact data for this specific battery on at what voltage the battery is at what state of charge but 3.5V should be around 10-15% at a very conservative top end. It could be much lower, but I also don't want to push it too far. I'd like to figure out if there is something I am possibly doing that is causing this calibration issue to happen. I am not charging mid-day unless it's low, I have not been playing games on the phone, I generally only charge on my wireless charger overnight, and use the phone lightly over the day.

Wait, this has happened before!

A few months ago I was using my Pixel Tablet as I do in the evening and it was at about 70% state of charge and I needed to reboot it for some reason. After it rebooted the battery showed 100%. I continued to use it for another hour or so, at which time it dropped to about 95%. When I put it on the dock it did not start charging since the battery status was over 90%. I have no idea why this happened, but I decided to go ahead and discharge the device to see if that'd fix it. I have no idea if it did, but battery life seems pretty normal on it currently so I just leave it alone.

Warning; don't do this unless you think you need to

Note that the whole exercise was to re-calibrate the battery state of charge with Android, cycling the battery itself is just the only way to do this and is not something you should regularly do as it's much harder on the battery to cycle a battery from 100 to 0. Ideally, it should be maintained between 60% and 80% but that's not reasonable on a phone, just keeping it from discharging below 40% daily will usually make the battery last a long time. However, Battery University still recommends an occasional re-calibration using the method I used here.

Summary

In the end, did I accomplish anything? Sort of; I think I now know my battery is probably okay or at least not as bad as I thought. It ran 40 hours and that is pretty reasonable with a bunch of apps updating their data, stuff syncing, etc.

But I'm also still not convinced the battery is in good shape. 40 hours is good but there's no way it can charge from 0% to 100% in 40 minutes. However, it was previously at 60% by lunch (4 hours after taking it off the charger) and now it's 60% late evening (15 hours after taking it off the charger). Still, I'm not quite sure what to make of all of this, but it is better than it was. I think what's going on is that the battery is worn out to some degree, but it was also very miscalibrated.