Hi guys!
I've been playing around with my GNex (GSM, stock 1750mAh battery) since last july and my biggest concern is (still) the battery life.
I've noticed that the couple stock rom + stock kernel (the ones the phone come with) is much better than any other custom rom+kernel.
Here comes my (maybe stupid) question: is the battery life somewhat related to the (de)odexed status of the rom?
I mean, I've been looking for all kinds of solutions to take advantage of those features offered by AOKP or PA without suffering from BL issues, but I find silly to sacrifice stability/smoothness/responsiveness/always-on-connection/brightness/whatsoever to gain not that many mins of juice. And I really wonder what is the sourcery Google adopts to make its roms so stable, responsive and battery friendly (e.g. no custom rom/kernel can achieve as much BL as the stock ones). Put differently, with the stock rom/kernel, I can leave 3G always on, auto-sync always on, haptic feedbacks on, location services always on (but GPS) and the battery survives for more than 24h; while, with custom roms/kernels, I could switch everything in the list off and still the battery wouldn't last that long (ceteris paribus).
Could you, please, explain me how it works?
Is there really no way to improve BL other than those listed above?
And, finally, does odexing the system apps (on custom roms) do the trick?
Cheers!
P.s.: the answers I'm looking for may already be in other threads.
If so, I apologize, but I tried googling different keywords many times, and got no interesting results.
For me the biggest source of battery drain is the screen by far. Maybe you enjoy custom ROMs more than the stock one and you keep the screen on more I would think that a custom ROM would be more battery friendly. Which ROMs have you tried?
Endriu90 said:
Hi guys!
I've been playing around with my GNex (GSM, stock 1750mAh battery) since last july and my biggest concern is (still) the battery life.
I've noticed that the couple stock rom + stock kernel (the ones the phone come with) is much better than any other custom rom+kernel.
Here comes my (maybe stupid) question: is the battery life somewhat related to the (de)odexed status of the rom?
I mean, I've been looking for all kinds of solutions to take advantage of those features offered by AOKP or PA without suffering from BL issues, but I find silly to sacrifice stability/smoothness/responsiveness/always-on-connection/brightness/whatsoever to gain not that many mins of juice. And I really wonder what is the sourcery Google adopts to make its roms so stable, responsive and battery friendly (e.g. no custom rom/kernel can achieve as much BL as the stock ones). Put differently, with the stock rom/kernel, I can leave 3G always on, auto-sync always on, haptic feedbacks on, location services always on (but GPS) and the battery survives for more than 24h; while, with custom roms/kernels, I could switch everything in the list off and still the battery wouldn't last that long (ceteris paribus).
Could you, please, explain me how it works?
Is there really no way to improve BL other than those listed above?
And, finally, does odexing the system apps (on custom roms) do the trick?
Cheers!
P.s.: the answers I'm looking for may already be in other threads.
If so, I apologize, but I tried googling different keywords many times, and got no interesting results.
Click to expand...
Click to collapse
Thats strange, to me battery life is better with custom ROMs and kernels
R: [Q] Battery life: stock VS custom roms and remedies
sirxdroid said:
For me the biggest source of battery drain is the screen by far. Maybe you enjoy custom ROMs more than the stock one and you keep the screen on more I would think that a custom ROM would be more battery friendly. Which ROMs have you tried?
Click to expand...
Click to collapse
Lol, maybe you're right!
Until now, I tried AOKP and PA roms and franco, AirKernel, GlaDOS and stock kernels (all possible combinations). I found that PA and GlaDOS are the best custom couple, but still not comparable with the factory ones.
However, even tough I have no technical numbers, the usage on custom stuff had been more or less the same as on stock things (although I became a pie-control addict). And what I know for sure, the BL gap is mostly due to screen (i.e. by staring at the launcher home screen for 5 minutes, the battery drains faster with custom roms than with stock roms - still, ceteris paribus).
NexusS4gFreak said:
Thats strange, to me battery life is better with custom ROMs and kernels
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Click to collapse
I know that's strange. Things used to work as you say with my HTC Desire. But since I've switched to the Nexus S (and then to the GNex), I strongly preferred stock stuff just because of battery life
Sent from my stockish Galaxy Nexus using xda app
Related
I'm an og droid user but just picked up a Dinc for my fiance. She loves the thing but hates the 10 hour (9 hours of that is idle?) battery life.
Last night, I went ahead and rooted it and removed most of the verizon crap-ware and then adjusted her sync settings to hopefully improve her battery life. I also did a battery stat reset.
She loves it as-is so flashing roms is out of the question. I don't have time/she doesn't have the patience for me to flash roms and fix problems that arise. With that being said I would like to explore the other back-end options.
Now, keeping in mind, this dinc is completely stock. Stock sense, stock kernel, stock radio, etc. I've been advised to replace the stock radio with one from Doug Piston. I was told to install the 04.08 version for the EVO. I just want to clarify that this will work for the Dinc running stock froyo sense? Also, if someone could tell me exactly what this does? Is the main benefit better battery life? Or something else? Also, if this is not the correct radio I should install, which is?
My second question is in regard to a better kernel. As stated above, I am stock and will remain on stock sense. What are some good proven kernels that will work on stock sense. Performance on the device is fine, so I'm not worried about that. I'm only looking for a kernel that will boost battery life. I looked around here but I couldn't determine which of these, if any would work on a stock Dinc or if they were just for custom roms?
Anyway, that's all. Thanks in advance for any help on this!
Here is a link to all the different kernels that are available for the Inc. It will say if it works with AOSP or Sense. Just take a look through them and see which one would work the best for what you want. Some will overclock, some will underclock, etc
http://forum.xda-developers.com/showthread.php?t=866736
Whoops didn't notice you had that link already. Some popular ones are incredikernel and heyitslou. I know with incredikernel I was getting good battery life but also was with different ROM not sense.
I have installed a radio on my Inc, been quite fine for the last few weeks as well. From my understanding, the radio may or may not improve gps lock and/or your phone's signal strength depending. This is hit or miss, not everyone notices a stark improvement in both or either category. As such, if you already have poor signal in your area it may not improve your signal therefore it has no effect on battery life.
Someone more knowledgeable in that area please correct me.
You can try whichever radio you desire, I recall many people using 4/08 or the 11/19. Personal preferences aside, your improved battery life depends on how much signal your phone reports that it is receiving.
I have used the heyitslou kernels and have loved the battery life I got with it. I have also upgraded my battery to the 3500mA battery. This did wonders
incredikernel w/ smartass + CM7 and never look back...i know you like the ROM but i think stock sense is what drains the battery the most.
I've had good luck with Lou's kernel running a sense rom.
may want to try Virtuous v3.2.0 its a good stock rom with some clean-up done.
So I am thinking that JB Roms are still in development and won't have good battery. Is there any good battery roms on ICS?
Also are there any gingerbread roms?
You would be thinking right seeing as jb just came out. Just search and see what people are commenting on, battery wise
DO YOU JELLY?
Can i have a ICS rom and a JB rom running on Boot Manager or do they have to be the same?
I also want to know the answer to this question.
There is no best battery ROM. each ROM behave differently. they will give good battery for some, and bad for others.
what do you reccomend?
It's really less about the ROM, and more about the kernel you use...whether you undervolt or underclock or not, how you set up your apps, and how you use your phone. I'm using mROM at the moment, with Franco's kernel, undervolted. I just swapped kernels today, so I can't speak to the battery life just yet.
Sent from my Full AOSP on Toro-VZW using xda premium
+1 on the kernel being important for battery life.
I chose AOKP for its high customization. Lots of ROMs are as smooth, or even maybe a little smoother than AOKP, but many are just way too bare bones for me. I find AOKP to be the best package for my style, allows for nav bar control, notification control and toggles for phone features in the notication tray and many many more things. Plus, on the market there are many AOKP theme apps like Kiwi Cobalt or Purple Kush that make your phone look saaaa-weeeeeet.
And I always run Trinity kernels on my Nexus for battery life. Not sure why, but they seem to give my phone the best life. I haven't had luck with franco or other kernels in that aspect. But every phone and setup is different.
The combo I am running is the best I have found for a perfect balance between great speed and really good battery life on my phone.
Just remember to do backups. :good: The most important thing I can recommend, especially if new to flashing/custom-ing like myself.
mattwilkinson11 said:
So I am thinking that JB Roms are still in development and won't have good battery. Is there any good battery roms on ICS?
Also are there any gingerbread roms?
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Click to collapse
I have NEVER tried this Rom.
But the Redemption Rom is supposed to be fast and have amazing battery life.
The catch is ZERO features. Just Stock. But that is why it's so fast apparently and have amazing battery.
Maybe u get to the Softkeys bar, I dunno.
Jellybean ROMs are smashing ICS in terms of battery life on the Nexus, and I think it may be a result of better RAM management. If you're just not ready to take the plunge on JB (source based ROMs are out now btw), and want a mix of customization, and battery life, CM9 may be the way to go. As for Gingerbread... hmmm... I doubt there are any ROMs available for the Nexus, and it sounds like a harsh, Benjamin Button type thing to do to such a great phone, lol.
Sent from my Full AOSP on Toro-VZW using xda premium
Here's my take on what really effects battery life:
As long as you have a ROM that doesn't malfunction and keep the phone active when it shouldn't be, all ROMs should get around the same battery life. If they don't, it's probably because you don't know about the difference in their settings - one might simply be using a more aggressive CPU governor. Even if you have a ROM that does absolutely nothing as much as possible, you are the cause of battery drain. I've tried all sorts of ROMs, and in the end, I'm the one causing battery drain. Whether it be me being sloppy and accidentally allowing too many background settings for apps, or me using more battery intensive features, I'm the one draining the battery in the end. From my experience, Stock, Liquid ICS, CM9, AOKP, Jelly Bean, Jelly Bean AOSP, any kernel you want to try, the user has the most affect on the battery life. Try adjusting your habits to improve battery life. I'm a heavy, heavy user (Sometimes with unlimited amperage from a 2.1amp charger, my phone still will die while charging.) I'm also in the Army, and when I know I will be in the field without power for extended periods of time, I change how I interact with my phone. Maybe don't overclock, even underclock/undervolt, use a more strict governor, even disable a CPU core, change Android settings to not allow ANY background apps, always turn off 4G and syncing, of course turn off BT and WiFi when not needed. I change from a user who can barely make it through the day to a user that can make it almost two. If you want something to give you better battery life without changing your habits, go buy a bigger battery or a newer phone.
Trinity 307 kernel all the way!!! Add in its conservative governor option and your conserving a lot of battery. Not to mention the kernel runs at a very low temp so your device will last well beyond the end of your 2yr contract plus it comes with a stock color mod thing that makes your gnex look amazing IMO.
I recently bought a used Sprint Galaxy S3, it is the SPH-L710 model.
It works great, I like it, I got it rooted with no problem, and got CWM flashed to it and I'm getting ready to flash a ROM.
I've been searching forums and sites for about 2 days for the ROM I want to use.
I'm mainly looking for something that enhances my battery performance, the reason for this is when I first got the phone, I updated it to the 4.4.2 KitKat when I first turned the phone on and the battery life was terrible, like I would charge it to 100% and use it browsing the web for about 10 mins and lose sometimes upwards of 10+% within that 10 minutes.
I searched around and found 2 Apps that I am using right now, one is a battery doctor type thing, the other is an app called Battery Saver (root) it changes some stuff and is supposed to make battery life better, since I have started using these 2 apps my battery life has increased, but it still seems to drain a little fast. So I would like to try and find a ROM that perhaps has tweaked the battery life.
Does anyone have any opinions on battery life for any of the ROMs here that would work for my device, like perhaps which one that you have tried that extended your battery life? I know I could just try them myself, but I am hoping to save a bit of time and see if anyone has some input.
Also another quick question, is there a way to test my battery and see if its just bad? A friend mentioned that the battery could have just gone bad so I'd like to check that if possible.
A. S3s aren't known for their amazing battery life. My battery does not go very far either, talking on the phone, which I do a lot for work, gobbles up the battery immensely. (Like 100% to 80% in 30 minutes.) Web browsing is another battery hog.
B. ROMs are only going to do so much as far as extending your battery life. Just bear in mind -- the lighter the ROM, the less battery it'll likely consume.
You'll do more to save battery by flashing a custom kernel on top of a light ROM that'll allow you undervolt/underclock. But, you want to make sure you flash the correct kernel to the correct ROM base (e.g. Touchwiz kernel for Touchwiz ROMs, AOSP/CM based kernels for AOSP/CM based ROMs).
I personally use the DKP kernel found here in the S3 original development thread.
Be careful w/ underclocking and especially undervolting, as this can cause the phone to freeze up. It's also important to choose a governor that has a nice balance between performance and power savings. (I like the freelunch governor.)
Hope this helps.
Higgs_Boson said:
A. S3s aren't known for their amazing battery life. My battery does not go very far either, talking on the phone, which I do a lot for work, gobbles up the battery immensely. (Like 100% to 80% in 30 minutes.) Web browsing is another battery hog.
B. ROMs are only going to do so much as far as extending your battery life. Just bear in mind -- the lighter the ROM, the less battery it'll likely consume.
You'll do more to save battery by flashing a custom kernel on top of a light ROM that'll allow you undervolt/underclock. But, you want to make sure you flash the correct kernel to the correct ROM base (e.g. Touchwiz kernel for Touchwiz ROMs, AOSP/CM based kernels for AOSP/CM based ROMs).
I personally use the DKP kernel found here in the S3 original development thread.
Be careful w/ underclocking and especially undervolting, as this can cause the phone to freeze up. It's also important to choose a governor that has a nice balance between performance and power savings. (I like the freelunch governor.)
Hope this helps.
Click to expand...
Click to collapse
Thanks!
That gives me an idea of what I should start looking for, and I'll check out the DKP kernel as well..
I just thought of another question I had, maybe you can help me with it too.
Since I'm running Android 4.4.2 on my device, would I need to find a 4.4.2 ROM to flash?
For instance could I use a 4.3.1 ROM on my 4.4.2 device?
vagabond007 said:
Thanks!
That gives me an idea of what I should start looking for, and I'll check out the DKP kernel as well..
I just thought of another question I had, maybe you can help me with it too.
Since I'm running Android 4.4.2 on my device, would I need to find a 4.4.2 ROM to flash?
For instance could I use a 4.3.1 ROM on my 4.4.2 device?
Click to expand...
Click to collapse
It doesn't matter which Android version you decide to go with. Just avoid two things:
1. Do not flash an older bootloader than the one you are currently on (e.g. If you are currently on ND8, do not flash any older bootloaders like MK5 or MD4).
2. Do not flash any modems older than the one you're currently on. Your modem version can be found in Settings -->About Phone --> and the last three letter/number combination under "Baseband Version". Hint: The baseband version also tells you which bootloader/ROM you're on.
Doing either of these, will trip Samsung's KNOX security feature, tripping the kill-fuse, and suddenly, you'll have yourself a nice hard brick.
I know that probably sounds intimidating, but I assure you if you avoid those two things, you can flash any D2LTE ROM you please. (D2LTE ROMs will work with the Sprint S3.)
idk man the batter life of my S3 lasts 2 days where my Infuse 4g would last less then one with a new battery.....so by far the best battery life I've had in a while
Higgs_Boson said:
It doesn't matter which Android version you decide to go with. Just avoid two things:
1. Do not flash an older bootloader than the one you are currently on (e.g. If you are currently on ND8, do not flash any older bootloaders like MK5 or MD4).
2. Do not flash any modems older than the one you're currently on. Your modem version can be found in Settings -->About Phone --> and the last three letter/number combination under "Baseband Version". Hint: The baseband version also tells you which bootloader/ROM you're on.
Doing either of these, will trip Samsung's KNOX security feature, tripping the kill-fuse, and suddenly, you'll have yourself a nice hard brick.
I know that probably sounds intimidating, but I assure you if you avoid those two things, you can flash any D2LTE ROM you please. (D2LTE ROMs will work with the Sprint S3.)
Click to expand...
Click to collapse
Wew! Thanks for that info, you may have saved me from a terrible mistake lol.
One of the ROMs I was looking at was using the MD4 bootloader, so that would have been a no-no xD
Thanks a lot for all your help, I learned a few things from it, epspecially about the bootloaders and modems having to match, I had no idea about that. Now that I know that, it opens up a few more possibilities for ROMs I can use!
vagabond007 said:
Wew! Thanks for that info, you may have saved me from a terrible mistake lol.
One of the ROMs I was looking at was using the MD4 bootloader, so that would have been a no-no xD
Thanks a lot for all your help, I learned a few things from it, epspecially about the bootloaders and modems having to match, I had no idea about that. Now that I know that, it opens up a few more possibilities for ROMs I can use!
Click to expand...
Click to collapse
Fun fact: The bootloaders and modems didn't always have to match.
Samsung wanted to be able to market their devices to business entities, and in order to do that, they developed the KNOX security feature.
Once it's on your phone, it's not coming off. It matters to corporate security policy people, because they want devices that aren't going to be compromised if someone tampers with them.
And, as you can see, the wrong kind of tampering makes the phone completely unusable and unrecoverable.
Higgs_Boson said:
Fun fact: The bootloaders and modems didn't always have to match.
Samsung wanted to be able to market their devices to business entities, and in order to do that, they developed the KNOX security feature.
Once it's on your phone, it's not coming off. It matters to corporate security policy people, because they want devices that aren't going to be compromised if someone tampers with them.
And, as you can see, the wrong kind of tampering makes the phone completely unusable and unrecoverable.
Click to expand...
Click to collapse
Right now I'm sort of leaning towards LiquidSmooth, Quantam4, or Tribute ROM, still sort of looking around though.
If you don't mind me asking @Higgs_Boson, which ROM are you using?
Also, to the other poster, my mothers GS3 is the same way, hers will last upwards of a day and a half, then again she doesn;t use hers for much, while I'm on mine like a computer lol.
vagabond007 said:
Right now I'm sort of leaning towards LiquidSmooth, Quantam4, or Tribute ROM, still sort of looking around though.
If you don't mind me asking @Higgs_Boson, which ROM are you using?
Also, to the other poster, my mothers GS3 is the same way, hers will last upwards of a day and a half, then again she doesn;t use hers for much, while I'm on mine like a computer lol.
Click to expand...
Click to collapse
Right now, I'm on CM11.
I usually switch between two that are my favorites:
CyanogenMod or Paranoid Android.
If you want an all-in-one, there is always PAC-ROM, which includes Paranoid Android, AOKP, and CM all under the same roof. (But then, we get back to that thing about light ROMs.)
issmal out
Higgs_Boson said:
Right now, I'm on CM11.
I usually switch between two that are my favorites:
CyanogenMod or Paranoid Android.
If you want an all-in-one, there is always PAC-ROM, which includes Paranoid Android, AOKP, and CM all under the same roof. (But then, we get back to that thing about light ROMs.)
Click to expand...
Click to collapse
I completely overlooked CM
Is CM11 compatible with the DKP Kernel you were telling me about?
yep
Yes it is. I'm that combo at the moment
im currently running wicked X 8.0
6th_Hokage said:
im currently running wicked X 8.0
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Click to collapse
I'm in the process of d/ing that right now. U like it?
jbnorton0524 said:
I'm in the process of d/ing that right now. U like it?
Click to expand...
Click to collapse
personally yes after i replace the system UI with the Stock ND8/NDC one and same with the TW Framework and TWframework-res.apk and use the Stockish theme for it.....i like the stock look what can i say but im using xposed at the same time for little things here and there but if you don't want to replace somethings and want it to work 100% use the PCB theme that it comes with.......but either way its pretty smooth and fast and the battery lasts for 2 days with some gaming and listening to music with viper4android installed and making calls and texting the one thing that i would say drains my battery is watching videos but you'll be satisfied
Wow you arent joking. This is one of the best ive seen lately. Nice.
jbnorton0524 said:
I'm in the process of d/ing that right now. U like it?
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Click to collapse
Wicked X, Tribute and Conquest Singularity are all 3 very good ROMs with pretty fair battery life. As stated, Kernal Settings do make a world of difference! I'm on Singularity with latest KT747 Kernal and love it :]
Cm 11 or paranoid
Hello,
What Custom Rom you guys think its best for Battery Life and Stability?
I've been using CM11 for the last few months and now im Trying Omnirom. They are both stable and use the same battery.
I cannot try every rom, so im asking here for your opinion.
I very much doubt battery life would be any different because of ROM version.
It has more to do with individual usage patterns
&
BT On/active/streaming
Brightness level/Auto
Data On/updates/push services
Calls talk time
Text/chat apps
Wi-Fi/Hotspot on/active
I'd say if your getting nearly 2h's of screen on time then the ROM is just fine.
There may be others getting more, but it all depends on how you use your device.
I don't mind charging my phone 2-3 times throughout the day(to help keep it topped up), I don't use Wi-Fi since I have unlimited data, unless it's for a large occasional download (testing new ROM/apps) have auto app updates and push services on) and leave BT on to automatically connect to my car stereo and start streaming music and also always leave auto brightness on.
Personally, I have tried lot's of different Custom Roms, and to be honest, none of them are as good as Stock 4.3 in terms of battery life and stability. Yes, other ROMs offer additional features and Android Versions that would otherwise be unavailable, but are mostly less stable, more laggy and have worse battery life. If you want customisation, you can root and use Xposed Framework.
That said!.. the best custom ROM that I have used is both FML Kitkat and FML Lollipop by MWisBest.
adamgraver said:
Personally, I have tried lot's of different Custom Roms, and to be honest, none of them are as good as Stock 4.3 in terms of battery life and stability... ...That said!.. the best custom ROM that I have used is both FML Kitkat and FML Lollipop by MWisBest.
Click to expand...
Click to collapse
Recently I went back to 4.2.2 (Verizon) because no roms I could find had decent battery life. I started using greenify to help with memory, as I find that soon as it gets to about 100mb free, the lag is terrible.
So in your opinion FML Kitkat vs stock on battery is worse? I briefly tried FML Lolipop but felt it was too early in dev and buggy
thx,
riz
Screensaver.tv said:
Recently I went back to 4.2.2 (Verizon) because no roms I could find had decent battery life. I started using greenify to help with memory, as I find that soon as it gets to about 100mb free, the lag is terrible.
So in your opinion FML Kitkat vs stock on battery is worse? I briefly tried FML Lolipop but felt it was too early in dev and buggy
thx,
riz
Click to expand...
Click to collapse
Yeah, I've always found that stock Jelly Bean has the best battery life. But your experiences may vary with usage.
I have used CM11, PA, Shiny ROM and FML so far. I cannot compare them to stock, since I haven't used stock due to lack of customization features.
IMO, Shiny ROM + Dirty V Kernel with Nephilim's settings had the best battery life. On standby, my phone ran for more than 2 days without a single charge. Performance was decent, although I wouldn't say that it was ideal.
I'm currently running on the latest FML Lollipop + Smitty L Kernel with Nephilim's settings. The battery life is decent, with about a day and a half standby time. Performance is fantastic. If you value both battery life AND performance, you might as well give this a try, as it is definitely worth the effort.
*If a good thread already exists about this, please link it.*
Hey Peeps!
I have probably tried all ROM's (Sense & Stock) on my aging M8, and the only ROM that comes with good battery life is ARHD. But, as we all know, it has its weaknesses.
Waiting for responses from you guys!
We do not compare ROM's that has the greatest etc. The best way to find it out is to try each ROM which fits you.
Sent from my HTC One_M8 using Tapatalk
There is no such thing as a ROM with "best battery life" that applies to everyone, in every situation. There are simply too many variable on how different folks use their phones (what apps, screen on time, etc.) your local reception, whether on LTE or 3g, WiFi, Bluetooth in use, etc. etc. etc.
Folks have very different experiences for each ROM. Seriously, I've seen some ROMs where I can get 2 days of light usage, where others on the same ROM will say battery life sucks and only lasts a few hours.
You need to use trial and error, and use what ROM works best for you. There are no shortcuts to that process.
XDA changed their rules some time ago to allow comparison threads as long as they dont turn into a flame war. Please keep this thread civil and respect everyone opinion.
Thanks
Wolf
redpoint73 said:
There is no such thing as a ROM with "best battery life" that applies to everyone, in every situation. There are simply too many variable on how different folks use their phones (what apps, screen on time, etc.) your local reception, whether on LTE or 3g, WiFi, Bluetooth in use, etc. etc. etc.
Folks have very different experiences for each ROM. Seriously, I've seen some ROMs where I can get 2 days of light usage, where others on the same ROM will say battery life sucks and only lasts a few hours.
You need to use trial and error, and use what ROM works best for you. There are no shortcuts to that process.
Click to expand...
Click to collapse
what type of effect does it exist on kernel with battery life?
what are the good & bad things of custom kernel? and also can kernel affect on radio?
umesh.lk said:
what type of effect does it exist on kernel with battery life?
what are the good & bad things of custom kernel? and also can kernel affect on radio?
Click to expand...
Click to collapse
I'm not that knowledgeable about kernels, and in particular don't mess much with custom kernels.
But what I would say, is that those questions aren't any more answerable then the previous points about custom ROM vs. battery life. Overclocking and undervolting allowed by custom kernels, as well as the choice of governors (which provide various balances of performance versus power usage) will all have some affect on battery life. But the experience is going to vary greatly from one user to another.
Similar to trying custom ROMs, just make a TWRP backup before flashing anything; try some custom kernels, or tweaking kernel settings; and see if the results are desirable to you.
The only real "bad" thing about custom kernels, is that some settings may result in instability, boot loops or no boot. But as long as you make a TWRP backup (before flashing kernels or changing kernel settings), you can easily recover from any such problems.
You also may or may not get the performance or battery life you are looking for, from custom kernels. Which is the main reason I've not been one to personally mess with custom kernels too much. With what kernel tweaking I did on other devices, I never saw a significant performance difference. And certainly not enough to warrant the hassles of system crashes and no boots I was getting.
But others will swear by custom kernels, different governors, etc. Again, your results can and will vary. So that is why its best to try for yourself; and not take another's advice as gospel.
Viper rom is quite good.