1. abhishek singh21's Avatar
    it takes only a moment for my lumia 730 battery to come down to 99% from 100%. even if unused. is this something unusual? the phone is only a weeks old.
    04-06-2015 08:45 AM
  2. gpobernardo's Avatar
    it takes only a moment for my lumia 730 battery to come down to 99% from 100%. even if unused. is this something unusual? the phone is only a weeks old.
    No, this is not unusual. In theory, a battery that is attached to a device that is using up its energy cannot remain at 100% as soon as it is unplugged from the charger... exactly because a device is using up its energy. It leaves 100% capacity as soon as it is unplugged.

    Having 100% displayed in the battery charge for several moments after the charger has been unplugged in certain devices is a result of the inherent deviations in battery circuit calibration*. Rounding off also comes into play, where 99.5% is rounded up to 100%.

    *- There has been an extensive discussion about this in the fora. Basically, modern rechargeable batteries in "high-tech" devices are equipped with circuits that protect the battery from overcharge and over-discharge and that estimate the amount of charge left based on the output voltage of the battery. That estimate is based on calibration data. If 4.2V = "100%" and 3.7V is "0%" (which it is not, otherwise there would be no output voltage at all), then the circuit interpolates every % value in between based on the voltage through some trend line. This trend line will become more accurate once the circuit has gathered enough data points (or enough "experience") on how the battery behaves with % charge. Hence, there is always a chance that this trend line and the estimate %charge the circuit gives are not 100% correct at all the times.
  3. gpobernardo's Avatar
    it takes only a moment for my lumia 730 battery to come down to 99% from 100%. even if unused. is this something unusual? the phone is only a weeks old.
    No, this is not unusual. In theory, a battery that is attached to a device that is using up its energy cannot remain at 100% as soon as it is unplugged from the charger... exactly because a device is using up its energy. It leaves 100% capacity as soon as it is unplugged.

    Having 100% displayed in the battery charge for several moments after the charger has been unplugged in certain devices is a result of the inherent deviations in battery circuit calibration*. Rounding off also comes into play, where 99.5% is rounded up to 100%.

    *- There has been an extensive discussion about this in the fora. Basically, modern rechargeable batteries in "high-tech" devices are equipped with circuits that protect the battery from overcharge and over-discharge and that estimate the amount of charge left based on the output voltage of the battery. That estimate is based on calibration data. If 4.2V = "100%" and 3.7V is "0%" (which it is not, otherwise there would be no output voltage at all), then the circuit interpolates every % value in between based on the voltage through some trend line. This trend line will become more accurate once the circuit has gathered enough data points (or enough "experience") on how the battery behaves with % charge. Hence, there is always a chance that this trend line and the estimate %charge the circuit gives are not 100% correct at all the times.
    04-06-2015 01:37 PM
  4. gomezz's Avatar
    Is this if the phone is taken off the charger as soon as is shows it is fully charged? I find that if I leave my phone on the charger for some time longer then it can go a couple of hours or more (without use) before it shows a drop below 100%.
    04-06-2015 02:38 PM
  5. gpobernardo's Avatar
    Is this if the phone is taken off the charger as soon as is shows it is fully charged? I find that if I leave my phone on the charger for some time longer then it can go a couple of hours or more (without use) before it shows a drop below 100%.
    Theoretically (again), the phone and/or the circuitry in the battery assembly should stop charging the battery as soon as the circuit detects that it has reached "100%" capacity, or it's full charge voltage. However, leaving the battery plugged in for a while after it is fully charged may alter the (active) calibration data in the circuit since it will have more data points for "100%". The calibration would then be slightly biased to 100%... you might observe that after remaining at 100% for a "long" period of time, the drop in % charge would be sudden and fast, which could be an effect of the calibration bias.

    The technical details are of course more in depth than this and not all batteries (and their circuits) are created equal, but battery manufacturers will most likely be reluctant in revealing their trade secrets as to how their batteries really work.
    Laura Knotek likes this.
    04-06-2015 02:47 PM
  6. gomezz's Avatar
    I should have added that I wait until the phone itself decides to stop charging as indicated by the Glance screen blanking (I have it set to show when charging) rather than when the battery indicator shows 100%. This sometimes means removing the phone from the charger pad then replacing to nudge the pad to resume charging after *it* thinks enough is enough.
    04-06-2015 04:01 PM

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