[Nexus 6  General] Vincent Adultman:
Long-time lurker, first-time poster. I've gotten a lot of good insight from reading posts and figured I would join to share what I've learned.

Its a long one and if you get all the way through it you will understand why.

Nexus 6 XT1103 with original battery running stock 7.1.1. Started showing issues in early 2020. Apps would be slow to respond. Camera would take forever to open and take a picture. Scrolling through news feed would be annoying because it would register my scroll as a tap into a news story. Weird static sound coming from speakers during scroll. Phone started to shut off on its own at around 20-30%. Installed Accubattery and it showed battery was at about half its original capacity. Progressively got worse throughout the year. Got to the point where it would shut off around 50% or even at 80-100% if opening something that would result in high CPU use spike. It was time to replace the battery.

Looked up battery recommendations. Ebay batteries seemed iffy. Initial install reviews would be fine but some reports of lasting for a year and then crapping out, or just no long term follow-up. Review of Akku Polarcell for a Nexus 5 seemed promising. Email to Wannasee was answered quickly. Batch of batteries they were offering was made in late 2019. They could have just made that up but I had no reason to doubt them. Looks like an actual brick and mortar operation. Ratings are pretty high. $10-15 for unknown battery off Ebay vs $35-40 for something made in 2019 from a reputable vendor. I decided to go with the Polarcell. Bought it after trying to open the phone up the first time to make sure I could. Could have bought the Polarcell from Wannasee’s store on Ebay. Waited for one of those mythical Ebay coupons to show up in my inbox but that never materialized, by which time the phone was really in bad shape. Compared the price for buying the Polarcell off of Wannasee’s Ebay store to buying directly from Wannasee’s site. Went with the direct buy since it was a buck or two cheaper with the exchange rate at that time and I didn’t have any Ebay coupons to use anyways. Paypal payment using credit card. Pay attention to currency conversion setting in Paypal. Was better for me to have my credit card do the conversion rather than let Paypal do it, but that’s because my card doesn’t charge foreign transaction fees. Came out to $36.68 when I bought it. Their email comm is pretty good. They let me know when it was going to ship, when it shipped, when it was expected to arrive and provided a tracking number.

By the time I was ready bite the bullet and buy the battery, the phone wouldn’t even recognize the charger. Went through multiple chargers and cords trying to figure that out. Seemed possible that it was cord or USB port related. Sometimes if the cord was held just so it would charge. Got to a point where it wouldn’t charge at all while on. Wouldn't even recognize the charger was plugged in. I did figure out that it would charge while off, but even that was hit or miss (more hit than miss though). Even while off it did seem like it wanted a higher output charger. I had been using a 1.5A HTC charger mainly. Eventually that didn't work. I tried 2A Samsung and that didn't work. A 4A Asus charger seemed to work the most reliably. So at this point I am debating whether its worth it to buy an almost $40 battery if something is seriously wrong with the phone. What made it worse was that my first attempt to open the phone ended up slicing through a flex cable part of the wireless charging coil. So I could have tried to figure out whether the charging issues were due to the USB port by trying a wireless charger, but not anymore! I was using plastic cards to separate the back from the frame; nothing metal. But the amount of force required to push through the glue was enough that when it broke through the card slipped and it was enough to slice through the thin plastic and copper of that ribbon. Irritating due to the loss of ability to troubleshoot the charging issue further, but I wasn't too burned up about it because I never use a wireless charger so I just took it out and left it out. Works fine without it, except of course no more wireless charging ability.

Looked up lots of videos on how to open up the phone. Most helpful ones were:

Most warn about the cable for the power and volume buttons; rightfully so. None mentioned the wireless charger flex on the opposite side. The power/volume ribbon did get a decent crease into it as well, but luckily no damage. Straightened it out and it works fine.

22 screws. They are tiny but they come out easily. Pretty much everything I read and watched said they were T4 screws, but at least with my screwdriver kit the T3 bit is the one to use. Besides getting the back off the rest of opening the phone to get the battery out was pretty simple. The videos say to separate the two halves of the power/volume ribbon where they intersect but I didn't have to do that. I just removed the end that plugs into the board. Seemed easier than messing with the tiny connector at the intersect and it was. Removing the battery connector didn't work how it should have. The plastic had become brittle with age and just broke apart when prying at it from the opening in the frame. Had to get under the frame and pry it off from the back side of the connector where the ribbon cable goes into it. By the way, by luck I had a decent charge on the old battery before removing it. More on why that was important later.

The Polarcell didn’t come with a curve in it like the OEM battery; it was just flat. But it wasn't hard to massage the edges down. Used the old battery as a guide to bend the new battery into shape. Other than that it went in just fine. Ribbon cable was already folded in the right direction so it just plugged right in. Frame went back into place without any interference. The phone turned on just fine. I dont remember if it charged while on that first time, or if I had charged it while it was off. Probably the latter. But it went to full charge. I did get a capacity reading from Accubattery so it was charging while on. It was in the low to mid 90s vs the rated capacity. That was worth it for me. The phone didn't shut off randomly anymore. The apps were quicker. The camera took pictures the way I remembered it used to. No more static noise. But the charging issue was still there.

The back came off a few more times after that as I tried troubleshooting as best I could to see whether there were any issues with the charge port. There were no visible issues. I did end up picking out some dust with a needle, but not any significant amount that would have explained why it wasn't recognizing being plugged in while on. I probed with a meter on the backside of the USB port while the phone was apart and plugged in to make sure voltage from the charger and cord was coming through. No issues there, but also not advisable to do. The contact points that need to be probed are very tiny and very close to other things. I was lucky I didn't short the 5V to anything important. Pretty sure I did short it at least once and it didn't do any damage, after which I stopped while I was ahead. Cleaned out the port with an old toothbrush dipped in isopropyl alcohol. That definitely seemed to help it charge more reliably while off, but it still wasn't charging while on.

I’ve read posts that suggested the charge port was bad and needed to be replaced, but the fact that the 5V was coming through the USB port meant it had to be something else. Before I had opened the phone up the first time and was troubleshooting this problem I had tried a full reset. Backed up the whole phone manually. It wasn't rooted at that time. At the same time I unlocked the bootloader to get ready to root it once I replaced the battery because I wanted to use a charge limiter with the new battery to extend its life (whether or not that actually works to extend the life I don’t care, its worth the tradeoff to me). The factory reset had made no difference to my charging issue. I had not reflashed the factory image at this point. I was just doing a factory reset with the image that was already on the phone.

After I replaced the battery and it was still having issues, I tried flashing the factory image. Even going in and wiping cache and data through stock recovery made no difference. In addition to charging issues while on there would also be connection issues. It would connect and disconnect if the USB cable was not held in the right way. Not the ideal condition to be flashing a ROM but I managed to keep it connected for long enough. This was not just once. I tried a couple different methods. The first probably was using the Nexus Root Toolkit. Then when that didn't work I went in and manually flashed each file with adb from the command line. At some point I had gotten it to a condition where I did not recognize what it was doing during boot and it was just sitting on the Google screen before the animation starts. Didn't realize then that it should not be on this screen for long. I let it sit like that overnight. I had it plugged in to a charger but I had no way of knowing whether it was charging… it was not. Drained the battery just sitting on that screen all night. Phone came apart again. Battery was down to 2.7V and the phone would not charge. Green light in the speaker came on once (I didn't even realize that light was there before this). It would charge a bit, screen would come on and then immediately die. Started looking up how to charge a Li-Po battery outside of the phone. Eventually my brain cells started working and I pulled out the new battery and put the old battery back in. It had a 4V charge in it still. Was able to get the phone to boot into the OS for the first time after the ROM flash. Turned phone off, pulled old battery out, put new battery in, plugged it in while it was off and it started charging. I kept the back off and had a fan blowing across it while it charged to make sure it didn't get hot. It charged to full. I pulled it out again to see that I hadn't done any permanent damage. It felt the same thickness as before. Nothing was swollen. Will eventually know for sure when I have some more charge/discharge cycles on it, but I think it will be fine since it wasn't discharged lower than 2.7V.

Phone back together. Still only charging while off. Last thing to try is what other posts were skeptical about working. Time to root in order to get access to the batterystats files. Tried to flash TWRP to recovery. It would take but it would not stick. Tried a few times and then gave up and moved on to installing Magisk without it. Turns out Magisk will work just fine with the stock recovery. Used Magisk to patch the boot image. Flashed the patched boot image with adb (still with a wonky USB connection that seemed like it needed to be held just right, but it was only 8meg so it flashed fast). Went with FX File Explorer to browse root. Navigated to data/system folder and moved the three batterystats files off the phone. Kept the files on my computer just in case something went south and I needed to put them back. Rebooted the phone. Booted up without any issues. Plugged in the charger. Recognized immediately and started to charge while on for the first time in a long time. But then it would do the same thing again where the next time I tried charging it would not. It would recognize its plugged into power but would not charge unless I turned the phone on. After a while I realized it would charge while on if I just rebooted it. I still haven’t figured out why this is happening, but its a minor inconvenience. Went through a few weeks worth of charge cycles and Accubattery is showing the Polarcell is at 95% health which seems good to me. I also installed Battery Charge Limit and set it to 80%. Whether or not that’s really going to extend the life of the battery I don’t know but its working fine for me. I get more than a full day out of it before I have to charge again, but I’m not really putting a heavy load on it.

This summarizes troubleshooting and fixing that spans at least three months, for an issue that has been going on for about a year. I’m sure a lot of the issues I had are interrelated. There were definitely a few red herrings along the way. There is no physical damage to the USB port or cables or chargers even though the behavior would have indicated there was. I’m sure the old battery caused issues with either corrupting the batterystats files or just loading it with bad data, and that somehow caused the charging issues I was having. That also seems like it was causing general connectivity issues via the USB port.

Normal people would not go through this much trouble for a 6 year old phone that was presenting so many problems. Safe to say I’m not normal. But I like fixing things and I don't like waste. Hopefully this experience, or at least portions of it, helps someone else keep their Nexus 6 going or maybe even other phones since none of the issue I encountered seem to be specific to the phone.