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  1. Thread Author  Thread Author    #1  

    Default Very bizarre charging behaviour from 2012 N7!!

    Ok I've not seen any threads quite like my issue, so I'll try to explain best I can. Ok, here I have an N7 (2012) wifi. Now, I work in electronics therefore know a bit about charging etc, so I've got the back off it to measure the voltage directly at the battery terminals. I have 4.2V across it - which is about as high as you want a 3.7V cell to reach at full charge. Also the unit (powered off or on, with screen off) is drawing about 17mA from my bench PSU (set to a 2.5A limit, @ 5.25V), which is what I'd expect of a full battery, along with the fact it's up at 4.2V.
    However, and this is the bizarre bit - unplug it, and the unit bleats away saying there's 5% battery left. So, back in with the power, it says charging. Leave the screen to go off. Check it about an hour later, the unit isn't switched on. Boot it up, it bleats again saying 2% left. Take out the power and put it back in. Charging again (allegedly). So I look in the battery section of settings to see what had occurred over this last hour or so... and according to the graph, while I had left the unit to charge, it rose from 5% to 15% over a period of around half an hour, then steadily DISCHARGED for the next half hour right down to 0, and switched off !! Situation now - it's "charging", and has been sat at 2% for about two hours. However, as expected, on another battery check, guess what - still at 4.2V - fully charged, about where it has been throughout. Well the lowest I saw it go was actually 4.13V.
    Any help would be appreciated here, as I can't see what the problem is, other than the battery is full and the os thinks it's empty. It was doing this on android 4.2, and I've since updated it to 4.3, and then 4.4.2. Same results, no change. I've also performed a factory reset via the os, and a hard reset (factory wipe/reset) via recovery. This is really strange, never come across this ever before. As I say, I've seen lots of battery issues experienced by N7 2012 owners, but nothing quite this odd!
  2. Thread Author  Thread Author    #2  

    Default Re: Very bizarre charging behaviour from 2012 N7!!

    Here's a screenshot of the evening:

    Very bizarre charging behaviour from 2012 N7!!-nex-screenshot_2014-04-29-00-49-55.png
  3. Thread Author  Thread Author    #3  

    Default Re: Very bizarre charging behaviour from 2012 N7!!

    Stranger and stranger. Long spell of charging, then it goes straight to 0%. So I leave it turned off for a while (not connected to charger), then turn it back on and miraculously it now has 32%! Which then jumps straight to 0 a few mins later. Now switched back on again, and it's back up to 24%!! See attached.

    Bizarre. Very bizarre charging behaviour from 2012 N7!!-screenshot_2014-04-29-17-43-00.png
  4. Thread Author  Thread Author    #4  

    Default Re: Very bizarre charging behaviour from 2012 N7!!

    Ok, so the winter's here and I've dug it out for another look. It updated straight away to 4.4.3, then 4.4.4. So I've run a few charge cycles and it's still largely similar - it will now only reach about 16 - 18% according to the os, but same as before, with a meter the battery itself is sat at 4.2V, but the os thinks it's 3.7ish V.

    The thing shuts down nearer to 0% now, at which time it reports around 3.5V, but measure it with a meter and it's actually at just on 4V. So the battery is charging just fine, and charging is shutting off correctly at 4.2V, but the os thinks its about half a volt lower.

    I'm guessing that because the os is reporting an incorrect voltage then no amount of calibration apps will be able to fix it? Any ideas at all?
  5. Thread Author  Thread Author    #5  

    Default Re: Very bizarre charging behaviour from 2012 N7!!

    Anyone? It can't be the battery surely, it holds its charge fine, even after a number of weeks. I've tried factory reset from both the os and from recovery, battery pull, everything.
  6. Thread Author  Thread Author    #6  

    Default UPDATE!

    OK I'm getting somewhere now! Here's a screenshot of the last few days from full charge. And yes it did fully charge, don't know how.

    My initial suspicion, looking at the chart, is the battery is fudged, especially going by the sharp troughs where it jumps significantly down and back up. Would anyone agree on that?
    Attached Thumbnails Attached Thumbnails Very bizarre charging behaviour from 2012 N7!!-screenshot_2014-12-29-12-29-58.png  
  7. #7  

    Default Re: UPDATE!

    I suspect your issue is not calibration, but you may as well want to try that. lithium battery charge circuits lose calibration over time, if the user partially charges and partially discharges. (Yes, using the battery between... oh, say 25% and 80% is good for the battery... but bad for calibration.) The solution is to recal the charge circuitry. You do this by using the device (tablet, phone, whatever... as long as it is using lithium batteries) until it dies from lack of charge. when this happens, try restarting it (most have a battery reserve function that shuts it down before you fully discharge.. which is often fatal) and let it die again. when you get down under 5 to 10 minutes of life, then plug in the charger and let it go to 100% without any interruption of that charge cycle. Basically, you are retraining the charge detection circuitry to correctly recognize empty and full. Many laptops come with instructions to do this on a regular basis.
  8. Thread Author  Thread Author    #8  

    Default Re: UPDATE!

    Yes I did try that, what I did was removed the battery and I unsoldered one of the cell tabs from the circuit for a minute, thus resetting the circuit (it didn't power up then until I reapplied power by means of the charger). However the sudden dips in charge concern me, it shouldn't drop from 87% to 36 and then back up again. Same happened a couple more times as you can see from the chart. I do believe it was left dead for quite some time before I was given it to look at, probably due to their having lost the charger and were attempting to use a 700mA phone charger with it - obviously insufficient !
  9. #9  

    Default Re: UPDATE!

    I don't know what the algorithm for calibration is, so couldn't say if disconnecting the battery is equivalent to discharging it as per the calibration routine. However, I'd suspect it works by essentially recording the battery voltages at low vs. high charge (which would explain how not fully charging/discharging on every use cycle would "un" calibrate it...) But, using the lower current phone charger shouldn't hurt it if it is a usb compatible phone. USB chargers all operate at 5V (the std USB voltage) so the lower current would just lengthen the required charge time.
  10. Thread Author  Thread Author    #10  

    Default Re: Very bizarre charging behaviour from 2012 N7!!

    OK now it's getting really strange! This is the latest battery chart.
    Attached Thumbnails Attached Thumbnails Very bizarre charging behaviour from 2012 N7!!-screenshot_2015-01-10-17-29-25.png  
  11. #11  

    Default Re: Very bizarre charging behaviour from 2012 N7!!

    The battery might be going bad--there could be some dendrite formation, as described by our resident 49th level tech wizard Rukbat: [GUIDE] Is My Battery Shot?

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