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Old 04-28-2012, 02:09 AM   #1
kimkindle
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Kindle Keyboard - Battery issues

Hi folks,

I have a battery issue with my Kindle Keyboard:

> gasgauge-info -c
Thu Apr 26 18:05:06 2012 INFO:battery charge 32%

Uptime in between approx. 15min - no WLAN/WiFi; no music; no reading; nothing but
the regular screensaver

> gasgauge-info -c
Fri Apr 27 01:26:04 2012 INFO:battery charge 6%

So my question is, what happened to my battery during this +5h?
After reloading I checked the battery status again and found out, that it has only? 96% almost immediately after the LED turned from orange to green - is this normal?

Thanks for Your help

Kim
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Old 04-28-2012, 02:34 AM   #2
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Yep, I think it's normal. Maybe you have a running process consuming CPU, but I doubt it. I guess this is to be expected by batteries in use. And the info they deliver isn't always that exact. As for stopping charging at 96% - that's also normal. Switching to green as a UI feature while continuing to trickle-load is quite common, too.
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Old 04-28-2012, 10:50 AM   #3
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Actually, for maximum lifespan, LiPo batteries should be kept between 40% and 70% charge. But we want maximum time between charges, which is why we "abuse" them by "overcharging" them to more than 70%.
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Old 04-28-2012, 01:43 PM   #4
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Yep, on the K3, the LED switches to green @ 95%.
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Old 04-28-2012, 05:56 PM   #5
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Quote:
Originally Posted by geekmaster View Post
Actually, for maximum lifespan, LiPo batteries should be kept between 40% and 70% charge. But we want maximum time between charges, which is why we "abuse" them by "overcharging" them to more than 70%.
I'd like to see some evidence for this. It's true that LiPos should be kept stored at around those percentages, but so long as you're using them, then there's nothing wrong with fully charging them.

In fact, by charging them more frequently, you are damaging the cells. More frequent charging than is necessary can be harmful.
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Old 04-28-2012, 06:32 PM   #6
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Also, keep in mind than from time to time, the framework likes to mess around with the index files, even if nothing's changed in the content, and the more books you have, the more CPU it'll eat. (That's kinda true as a whole too, since it'll churn a bit on the index file every time it wakes up from sleep, too).
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Old 04-29-2012, 02:29 AM   #7
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Quote:
Originally Posted by ChrisKaos View Post
I'd like to see some evidence for this. It's true that LiPos should be kept stored at around those percentages, but so long as you're using them, then there's nothing wrong with fully charging them.

In fact, by charging them more frequently, you are damaging the cells. More frequent charging than is necessary can be harmful.
Actually, I meant LiOn, not LiPo, but even so, lithium battery lifespan is a complex subject. Every time you charge it you reduce its lifespace. Sitting new in its original box reduces its lifespan. Buying a spare lithium battery is not useful because when your first battery goes dead, the spare is nearly dead as well. Fast battery chargers (one hour or less) like the kindles use typically skip stage two of the lithium charge cycle and go ready (green LED) at 70% capacity. They may continue to trickle charge to full capacity, but this can reduce lifespan due to metallic lithium plating. Batteries rated for long life (military and medical applications) are specified with a lower operating (full charge) voltage for the same chemistry. The lower charge voltage increases the lifespan. But for consumer devices, it is more common to give a full topping charge to the higher specified voltage, and just let the battery have a shorter lifespan. This is why cellphone batteries have such a short lifespan (to make each charge last longer). You can read more about this from many different websites...


Last edited by geekmaster; 04-29-2012 at 02:32 AM.
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