There is a battery issue for Samsung Galaxy S2 i777.
The battery level will sometimes drop down abruptly after restart.
I restart my phone when the battery level is 40%, for example. After restart, the battery level drops down to 20%, in just seconds of restart.
See the screen captures
See the abrupt drop down?
This issue exists both in Android 2.3.6 and 4.0.3
I don't know if it's the software or hardware problem. Who can tell me?
Thanks.
zacling wrote:Thank you all guys for replying my post.
Actually, I factory reset my phone several weeks ago. But the problem persists.
It's not a real problem - it's just a small glitch. Remember, you didn't suddenly "lose" 20% of battery out of nowhere. If your battery actually had that much true capacity disappear in that short of an amount of time - it would have heated up to the point that it caught fire.
That drop isn't real - it's just the fuel gauge reporting artificially low in a particular corner case it doesn't handle well. The fuel gauge algorithm has certain assumptions, and a heavy load immediately after a reset invalidates those assumptions so makes the gauge report artificially low. It's not a software issue, it's a fundamental limitation of the hardware. It is what engineers call a "corner case" - Rebooting on low battery is one of the only cases where the fuel gauge chip gets thrown off and inaccurate. In this case you'll probably notice that after the drop it'll hold level for a while and may even start reporting increasing battery state of charge estimates for an hour or two.
Other fuel gauge chipsets won't get confused in this one situation, but they will become increasingly inaccurate over time, requiring periodic "calibration" cycles - 2-3 full discharge/recharge cycles. Such calibration cycles are not required on any Galaxy S1 or S2 family device. Not sure about the S3 family.
I forgot to look up how to do the fuel gauge reset process last night... I'll try to look it up when I remember.
Edit: I looked it up... Sorry, it can only be performed on a rooted device. On a non-rooted device, just wait and it'll become accurate again over time.
On a rooted device, it can be done from a terminal emulator shell by running the following:
echo "1" >/sys/class/power_supply/fuelgauge/fg_reset_soc
(looks like this forum doesn't support [code] tags. 
Entropy512 wrote:
zacling wrote:Thank you all guys for replying my post.
Actually, I factory reset my phone several weeks ago. But the problem persists.
It's not a real problem - it's just a small glitch. Remember, you didn't suddenly "lose" 20% of battery out of nowhere. If your battery actually had that much true capacity disappear in that short of an amount of time - it would have heated up to the point that it caught fire.
That drop isn't real - it's just the fuel gauge reporting artificially low in a particular corner case it doesn't handle well. The fuel gauge algorithm has certain assumptions, and a heavy load immediately after a reset invalidates those assumptions so makes the gauge report artificially low. It's not a software issue, it's a fundamental limitation of the hardware. It is what engineers call a "corner case" - Rebooting on low battery is one of the only cases where the fuel gauge chip gets thrown off and inaccurate. In this case you'll probably notice that after the drop it'll hold level for a while and may even start reporting increasing battery state of charge estimates for an hour or two.
Other fuel gauge chipsets won't get confused in this one situation, but they will become increasingly inaccurate over time, requiring periodic "calibration" cycles - 2-3 full discharge/recharge cycles. Such calibration cycles are not required on any Galaxy S1 or S2 family device. Not sure about the S3 family.
I forgot to look up how to do the fuel gauge reset process last night... I'll try to look it up when I remember.
Edit: I looked it up... Sorry, it can only be performed on a rooted device. On a non-rooted device, just wait and it'll become accurate again over time.
On a rooted device, it can be done from a terminal emulator shell by running the following:
echo "1" >/sys/class/power_supply/fuelgauge/fg_reset_soc
(looks like this forum doesn't support [code] tags.
Thank you Entropy512 for your info.
Last night, when the battery level was about 25%, it powered off automatically and cannot powered on.
Then I took the battery out and put it back and powered it on. The battery was only 3% by then.
It's really annoying.
smooth4lyfe wrote:Did you try the Juice Defender app?
There are a lot of things going on in Android which it can better control than Android alone....hopefully it will be fixed in Jelly Bean
Once I used a battery saver app but it worsen the battery life so I do not so trust such apps.
But maybe I should try Juice Defender. Thank you for your recommendation. 
Entropy512 wrote:
smooth4lyfe wrote:Did you try the Juice Defender app?
There are a lot of things going on in Android which it can better control than Android alone....hopefully it will be fixed in Jelly Bean
Don't expect it to be... AT&T always manages to horribly mangle firmware releases. Everything I've heard indicates UCLE5 was an epic disaster. I haven't gone near it myself... I'm currently running CM10 on my I777.
Is CM10 stable on i777? How do you feel about the CM10? Do you have a download link? Thank you.
zacling wrote:
Entropy512 wrote:
smooth4lyfe wrote:Did you try the Juice Defender app?
There are a lot of things going on in Android which it can better control than Android alone....hopefully it will be fixed in Jelly Bean
Don't expect it to be... AT&T always manages to horribly mangle firmware releases. Everything I've heard indicates UCLE5 was an epic disaster. I haven't gone near it myself... I'm currently running CM10 on my I777.
Is CM10 stable on i777? How do you feel about the CM10? Do you have a download link? Thank you.
CM9 is, but CM10 is still pre-alpha... cyanogenmod.com - Note that installing custom firmwares like CM WILL void your warranty.
