Will I get back my old kernel?
I am rooted with an unlocked bootloader and have flashed a variety of ROMs since I got my phone but have always kept the stock kernel. I recently flashed the VRUCML1 rooted ROM from XDA in which I included the imoseyon kernel. I just can't get my battery life where I need it and don't fully understand the bit about the kernel.
If I nandroid back to my previous ROM with the stock kernel will I indeed get my old kernel back or will I need to flash the kernel independently? Also if I flash other ROMS such as some of the 4.4 stuff floating around will those include a new kernel or again, will that be a separate flash?
Re: Will I get back my old kernel?
Each rom comes with a kernel when you flash it. Afterwards you can flash a kernel that's different than the one that came with your phone. If you like the rom you're using now but want the kernel that came with it, just flash the rom again without wiping. Make sure to do a back up before you flash the same rom.
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Re: Will I get back my old kernel?
When you restore from a nandroid backup, you'll get whatever kernel that was running at the time you made the backup. But there's more to battery usage than just the kernel, although it is the kernel and not the ROM that sets the battery usage. I do use the Lean Kernel, and recommed it for lower battery usage, but in addition to using the Lean Kernel:
1. A lot of de-bloating using Titanium Backup. I have frozen a lot of apps that I don't use, including the Google Services Framework and Google Play Services. I haven't frozen Google Play Store, since I noticed that Titanium Backup uses it sometimes to check it's license. When I tried freezing the Play Store, Titanium Backup froze because it couldn't verify it's license. But I don't miss Google Services Framework or Play Services...I do manual syncs infrequently, and don't care about notification from apps, other than for text messages, of course. The only app that I have that misses these is Google Maps, and it does request Google Play Services, although I find that Google Maps runs fine without it. I do unfreeze the Google services framework and play services about once a week to get app updates *smile*. I hear that I wouldn't even need to do that if I got my apps from Amazon, but I'm not currently doing that. In the same spirit, I'm using Boomerang Mail instead of Gmail app, because I like the way that it refreshes email when I open it, and works well. That way I don't have to manually sync my email, Boomerang does it automatically when I want to use it.
2. Using greenify and the xposed framework for a hibernating a limited number of apps between uses...without that, they would continue to run in the background. At this point, I have only Google Maps, Google Play Store, Chrome, and Factory Mode greenified, which are apps that often seem to be running in the background. You can add apps as you figure out what's using up your battery by continuing to run in the background when you're not using it.
My idle battery usage is running about 1% per hour, which is fine with me. A couple of good tools to look at battery usage are "wakelock detector" and "betterbatterystats". These allow you to see how much deep sleep that your phone is getting; i.e. how much it is sleeping when idle, using less battery, as opposed to be held awake by particular apps. And they help you find out what apps are waking up your phone so that you can do something about it if you want to.