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Old 04-23-2021, 05:12 AM   #1
atonement
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Is it possible to limit battery charge to say 80%?

In my rooted Android devices I have faithfully adhered to limiting charge between 30-80%. Probably that's why even after 4+ years in 2 of my oldest devices (2 & 3 years of intensive usage) battery health is still in the 85-90% range and they still deliver 8-10 hour SoT. Considering the difficulty in obtaining a replacement battery for Kindles in my country I would like to prolong the battery life as far as possible. After jailbreak I have no desire to get an Android based one.
Is this possible? Thanks.
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Old 04-23-2021, 09:45 AM   #2
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Nope. But the PMIC will take care of that for you anyway (roughly speaking).
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Old 04-23-2021, 10:00 AM   #3
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Oh. Do you mean by faking battery charge levels or something else?
Also once fully charged and plugged in does the device take power from the mains or from the battery? I couldn't determine it.
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Old 04-23-2021, 11:21 AM   #4
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It will definitely stop charging on its own.
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Old 04-23-2021, 01:03 PM   #5
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Quote:
Originally Posted by atonement View Post
Also once fully charged and plugged in does the device take power from the mains or from the battery? I couldn't determine it.
Once the PMIC decides the battery is charged, the current to the battery stops and the kindle is powered from the charger. There are numerous inexpensive USB power meters that display voltage, current, and sometimes more. Some information is available from the kindle in /sys/class/power_supply/max*battery/

See more information below.

Quote:
Originally Posted by atonement View Post
In my rooted Android devices I have faithfully adhered to limiting charge between 30-80%. Probably that's why even after 4+ years in 2 of my oldest devices (2 & 3 years of intensive usage) battery health is still in the 85-90% range and they still deliver 8-10 hour SoT. Considering the difficulty in obtaining a replacement battery for Kindles in my country I would like to prolong the battery life as far as possible. After jailbreak I have no desire to get an Android based one.
Is this possible? Thanks.
I tried to do that a few years ago. It is easy enough to stop charging at some arbitrary percentage below 100, but that also stops powering the kindle from the charger and I
could not come up with a way to command powering the kindle from the charger without resuming charging. I also could not come up with a way to automatically resume charging while the kindle is sleeping.

I have a script to print battery status information. The following works on Voyage and PW3. For Oasis 2 or 3 change max77696-battery to max77796-battery
Code:
#!/bin/sh
DATE=`date '+%Y-%m-%dT%H:%M:%S'`
MA_NOW=`cat /sys/class/power_supply/max77696-battery/current_now`
V_NOW=`cat /sys/class/power_supply/max77696-battery/voltage_now`
MA_AV=`cat /sys/class/power_supply/max77696-battery/current_avg`
V_AV=`cat /sys/class/power_supply/max77696-battery/voltage_avg`
PCT=`cat /sys/class/power_supply/max77696-battery/capacity`
CHRG=`cat /sys/class/power_supply/max77696-battery/charge_now`
TBAT=`cat /sys/class/power_supply/max77696-battery/temp`
echo "$DATE $PCT $CHRG $MA_NOW $MA_AV $V_NOW $V_AV $TBAT"
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Old 04-24-2021, 08:01 AM   #6
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After hitting 100% battery just kept on charging. Design capacity 1408mAh but it had reached 1458mAh. I was anxious about overcharging so ultimately unplugged it.
While Android devices charge at upto 4.4V, Kindle only reached 4.19V. Every 0.1V decrease in max. charging voltage is supposed to potentially double the useful cycle count. So it's a bit better.
In many Android devices a charge control file is present where with root it's trivial to start/stop charging by changing the value from 0 to 1 and vice-versa.
When plugged in and at 100% battery status was shown as "Full" vs "Discharging" when it's unplugged.
I use the Battery Status KUAL extension in my PW3. Works well. Best feature is the battery temp. readout. No more prolonged reading under direct sunlight!
Cycle count is still only 13 after 1.5 years which is nice. But recently the battery in my 33 month laptop with only 48 cycle count has significantly degraded such that it no longer charges beyond 80% or so and falls to zero straightaway from 20-25%.
P.S. For some older Kindles there was a software mod to boot the device without a battery. Does that still work for newer devices in particular the PW3?
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Old 04-25-2021, 05:19 AM   #7
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Quote:
Originally Posted by atonement View Post
P.S. For some older Kindles there was a software mod to boot the device without a battery. Does that still work for newer devices in particular the PW3?
The Paperwhite 3 starts without problems without batteries. Just add a 100k resistor pretending to be a temperature sensor. This applies to all kindle with 3-pin batteries.

Last edited by eddie.t.h; 04-25-2021 at 05:21 AM.
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Old 04-25-2021, 06:07 AM   #8
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Thats good to know. Is there a guide or tutorial for the same? Thanks.
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Old 04-25-2021, 06:26 AM   #9
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I haven't seen a tutorial for this anywhere. Just connect it like in the picture. Resistor ~ 100k, power supply max 4.2V.
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Old 04-29-2021, 02:18 AM   #10
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I definitely agree it's worth trying. But I heavily used my voyage (tried to read every day) during the last 6 years, the battery is still not a concern to me. The battery must decay after years of service, but voyage can still last for weeks.
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Old 04-29-2021, 06:12 AM   #11
atonement
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That's good to know. What's the battery cycle count?
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Old 04-29-2021, 07:53 AM   #12
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"U-Boot 2014.04 (Mar 19 2020 - 22:30:49)

CPU: Freescale i.MX6SL rev1.3 at 792 MHz
CPU: Temperature 30 C, calibration data: 0x5774f95f
Reset cause: POR
FRED::: EXTCSD177=0, 179=48FSL_SDHC: 0, FSL_SDHC: 1, FSL_SDHC: 2
Board: Heisenberg
Board Id: P00118077426092X
S/N: G000K90574260B56
I2C: ready
DRAM: MR5=0x1,MR6=0x4 512 MiB"

Is it possible to get CPU temp. at least by a terminal command or something else? Didn't know where else to ask...
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Old 04-29-2021, 01:25 PM   #13
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Is it possible to get CPU temp. at least by a terminal command or something else? Didn't know where else to ask...
Did you read post #5 in this thread?
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Old 04-29-2021, 01:42 PM   #14
atonement
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That's for battery temp, isn't it?
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Old 04-29-2021, 01:46 PM   #15
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That's for battery temp, isn't it?
Yes. Sorry.
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