I spent about 14 months without touching my S3 mini, and messing around with it. Very recently however the battery started draining out immediately after a phone call so I was desperate to fix the issue. I’m nowhere near a phones expert, but every problem has its solution and this is what I wanted to find out. So first thought of eliminating any issues that may have been software related. After installing and unistalling numerous apps, it was time for a phone OS update. S3 mini is shipped with Android 4.1.1 (aka JellyBean) so I was looking to update to 4.4.2 (Kit Kat stable version). If the issue persisted it would be time for a new battery I guessed. I know that i’m talking specifics here and the process may apply to other phones but I own an S3 mini so here goes each step I followed:
1. Back up the entire phone. Few tips on this include, fully utilizing your google account for contacts and calendar, storing every media in SD card and keep an up-to-date Play Store account. All other stuff like texts, need to be specifically backed up. For texts I used SMS Backup & Restore. I was also pleased to find out that Whatsapp messages are stored in the cloud so once you reinstall and connect to your account you lose nothing.
3. Turn your phone off and reboot in download mode. You can do this on Samsung Galaxy by pressing and holding volume down, power and menu button all at the same time until warning appears on screen. Press volume up button to enter the download mode.
4. Run Odin3 on your PC and connect your phone to your computer. ID:COM box will turn either blue or yellow once it detects the phone.
5. Click on PDA button (…in Odin3) and select the CF-Autoroot file already downloaded in step 2. Click on start button to begin rooting.Your phone will restart a few times during the process. Wait until rooting completes and when ID: COM box turns green along with pass message displayed on the screen, unplug phone and restart it in normal mode.
To install the Recovery tool
1. Switch off your device and then switch on in download mode just like told above.
2. While Odin3 is running, connect your device again with computer after which ID: COM box shall turn yellow. Now select the CF recovery file by clicking on PDA button. Make sure that only F.Reset and Auto Root options are checked while all other are unchecked. Now hit start button to begin installation. Wait until CWM recovery installs in Galaxy S3 mini and then disconnect it from computer. Reboot it in normal mode and you have CWM installed in your smartphone device.
Installing new rom
After following these steps your phone should be rooted and you are free to install any custom ROM suitable for your phone. In my case, after looking around a bit I went for CyanogenMod 11 which would bring Android Kit Kat on my s3 mini
2. Now remove the USB cable and and switch your S3 Mini off.
3. Go in to the Recovery Mode, to do that press and hold the Volume Up button, Home key and Power button all at the same time. Release the buttons as soon as you see the Samsung logo.
4. Once entered into Recovery Mode, head to Backup and Restore and then select Backup. This will perform Nandroid backup and will come in handy if anything goes wrong.
5. Now clear out the data by selecting Wipe Data/Factory Reset. Once the process is complete, select Wipe Cache Partition and lastly go to Advanced and then select Wipe Dalvik Cache.
6. Now go back to the main menu and select Install Zip From SDcard and then select Choose Zip From SDcard. Browse to the location where you put the CyanogenMod 11 zip file and install it.
7. Repeat the Step 6 to install Gapps as well.
8. Now select Reboot System Now from the main menu. The first time boot may take few minutes so be patient.
After doing all this, battery issue still remains. Another big issue of this version of the room is that it’s got some issues such as no 3g network connectivity. I hope that future releases of this rom will fix this problem.