Touch Battery Indicator is not accurate

[Smartie]

When I woke up touch this morning. the battery showed 88%, then I plug in my computer, the indicator showed 95%. I just woke up touch again, it showed 72%. I charged it by wall charger, it shows 100%. How to fix it? This is software issue or battery issue?

Thanks

[JSWolf]

One way to try to fix a battery meter that's not displaying the correct amount is to charge the battery until it shows that it is charged. Unplug the charger from the device and plug it back in. Keep doing this until the device takes 1 minute or less to charge to full. This would mean the battery is charged and the device will also think the device is charged, thus calibrated.

[Smartie]

Originally Posted by JSWolf

charge the battery until it shows that it is charged.

THanks.

If it shows 100%, does that mean it is charged ?

[JSWolf]

On most Readers I've used/seen, there is an LED that lights up. It either changes color or goes off when charged. I don't know about the Kobo. I've not seen the newer ones in person yet.

[TechniSol]

Was it used after charging it? Dropping from 90+ if powered off to 70 something seems a bit odd.

The thing you must remember is that the charge percentage being displayed appears to be an interpolated value(more like a guess in this case) based on the voltage level as measured near the battery. When the device is charging the higher incoming charging voltage skews the reading which explains why it often drops a bit if you unplug before charging has completed. I suspect the interpolated value gets to 100% a bit before charging is finally terminated because the Kobo tends to stay at 100% for a considerable period during discharge and rapidly diminishes somewhere below 30% -in my experience.

[Ken Maltby]

Li-ion batteries have a termination stage as they can be damaged if trickle charged after they have reached "full charge". The three charging stages make it so that an exact measure of the charge level at any time, is not practical. Any measurement prior to termination is just an approximation.

Luck;
Ken

[TechniSol]

Agreed, final termination voltage varies which explains why the top end is off or cushioned, but the 30% or so falloff towards zero is waaaaaay off on the lower end of the scale. You'd think they'd at least build a mechanism that's somewhat self correcting into the interpolation process when it's so far off or implement a better fit curve initially. Maybe it just comes down to the idea that you should probably charge Lion before you get anywhere near the low end...

Frankly, all in all, it's probably not so important to be accurate as it is for it to be consistent.

[Smartie]

Sorry not familiar with it,but this mean battery is start to die or just measurement ?

Thanks

[Ken Maltby]

A battery monitoring script tshring wrote that you can run with his Kobo Start Menu. If you have it running while you charge your Kobo, you will see charging data updated every minute. The way the charging process works it will get to a point where the number stops increasing, that is as it should be, wait until it jumps to 100and and says "Not Charging". It may take some time between when the number stops increasing and it jumps to 100, that is as expected.

Luck;
Ken

[JSWolf]

But you have to sometimes calibrate the reader to the battery and the only way to do that is to do the minute charge like I've explain previously.

[Aydan]

A "proper" LiIon-Battery fuel gage measures the voltage to know if the battery is completely full or completely empty and integrates over the current going in and out of thew battery. By monitoring the current it will, in theory, always know the charge in the battery.
In reality there's measurement tolerances, self-discharge, aging and so on that introduce a drift between what the battery gage thinks the charge of the battery is and the actual charge.
A proper calibration cycle measures a full charge cycle from completely empty to completely full and a full discharge cycle until empty.
The question is what type of battery gage the Kobo actually has.
If I remember correctly the sysfs tree doesn't expose the charge current which leads me to suspect that Kobo's battery gage doesn't measure the current but estimates the charge from the voltage. And this will always be very inaccurate.

Regards
Aydan

[JSWolf]

That's why you sometimes have to do the calibration by charging until it takes 1 minute or less to get a full charge. I had to do that recently on my 650 as it go lost because of all the very short plugins I was doing to add more books.

[Aydan]

Originally Posted by JSWolf

That's why you sometimes have to do the calibration by charging until it takes 1 minute or less to get a full charge. I had to do that recently on my 650 as it go lost because of all the very short plugins I was doing to add more books.

That shouls not actually be necessary. As soon as the charge controller has finished stage 3 of the charge process, the battery has a known state of "full". Repeatedly plugging in the charger will only reduce the lifetime of the battery. This will also not calibrate the usable charge of the battery, as soon as you discharge the battery near empty, the gage will be off again, becaus it "recalibrates" on the empty state.

Regards
Aydan

[JSWolf]

Originally Posted by Aydan

That shouls not actually be necessary. As soon as the charge controller has finished stage 3 of the charge process, the battery has a known state of "full". Repeatedly plugging in the charger will only reduce the lifetime of the battery. This will also not calibrate the usable charge of the battery, as soon as you discharge the battery near empty, the gage will be off again, becaus it "recalibrates" on the empty state.

Regards
Aydan

But the battery meter gets it wrong and thus thinks the battery is at a different state then it really is. So as the battery drains, the meter shows this at a different rate then it really happening. Thus, the calibration which is needed to fix this.

[Aydan]

If you think it is worth to expose your battery to an exessive number of charge cycles just to "calibrate" a badly implemented battery gage, be my guest.
Myself, I don't really care if the battery gage is off by 10 or 20 percent, at least for the kobo.

Regards
Aydan