I was very disappointed when I tried to install Pokemon Go on my Samsung Galaxy S2 and got an "error parsing the package" or "parseerfout" in Dutch. In the Google play store you probably get "your device is not compatible".
This is all due to the fact that the Galaxy S2 only got upgrades to Jellybean (android 4.1.2) and you need a minimum of 4.4 (KitKat) to play Pokemon Go.
BUT! you can still play pokemon go on your galaxy S2, but you will have to upgrade it yourself to KitKat (4.4). In the steps below I will explain how I upgraded my own galaxy s2.
And playing Pokemon Go for some days now :)
In order to upgrade your Galaxy S2 yourself to android 4.4 KitKat, you will have to root your phone.
No, don't run away now, it is actually a piece of cake.
When you root your phone, your warranty expires.. however it has expired a long time ago so you don't need to worry about that anymore! :) But I must emphasise that rooting and upgrading is at your own risk. If you follow the steps to the T, everything should go fine.
And also after rooting: make a nandroid backup (will be explained) so you will always have a working phone to fall back on in case something happens for some reason.
First read all the steps before you start, so you know what you can expect.
Please note that this guide is for the Samsung Galaxy S2 GT-I9100. If you have any other model, it may not work and you risk bricking (damaging) your phone making it useless.
So, also check your model!
It may also work for other models, but then you will need to download the specific ROMs for your model.
and.. everything is at your own risk.. but you will be able to play Pokemon Go on your samsung galaxy S2, wouldn't that be great! :)
STEP 1 - ROOTING YOUR PHONE
I followed the dummies guide to root your phone. You can find it here.
Follow it to the T, and your phone will be rooted :) it is really written for dummies, piece of cake!
One note from my experience: it may take some time in the odin step to get the green bar.
Mine seemed to be stuck on blue (reboot) while my phone had already rebooted.
But BE PATIENT. Really wait until you get the green bar (may take 30sec to minute after your phone rebooted itself and started up).
STEP 2 - MAKE BACKUPS
It will be NECESSARY to make a backup of your phone.
Make 2 backups:
1) Nandroid backup (to be able to restore to this exact state in case of any trouble)
2) Helium (app) or Titanium (app) backup (to be able to put all your apps, settings etc back after you updated to the new OS)
3) Contacts. check how your contacts are stored.
1) Nandroid backup
open the CWM app (in your appbox) and select make a backup. check afterwards with going to restore if you can indeed see your backup (or navigate to the folder to see if it's there)
If it's not working go to restart in restore mode (option in CWM), and you will be able to create a backup there.
2) Helium / Titanium backup
Download one of these apps. I myself used helium, and worked fine. Do select the large backup, that also the apps itself will be put back in your phone. Otherwise it will only save the data and you will need to install all the apps yourself. It also back-ups your wifisettings & passwords, and also your whatsapp & facebook data, but for the latter you still need to download the apps afterwards. Only my experience is with helium that I also selected that all my messages (SMSs) are back-uped, but these were gone after putting everything back..
I don't have experience with titanium, but it seems a good (maybe better app) than helium.
3) Contacts. check how your contacts are stored. Mine are on my simcard so no need to backup, but check if yours are on your phone. If they are, they need to be backed up (eg with the KIES program from the step 1 rooting).
STEP 3 - DOWNLOAD KITKATcompatible CWM, kitkat rom & gapps
The CWM recovery version that comes with the Kernel you used in rooting the phone, is too old for installing KitKat. So before KitKat can be installed, a new kernel needs to be put in.
* Download the new kernel (.zip) here. The downloadlink is on the bottom of the page.
This kernel is not compatible with the OS you have now, so we will also already put the new ROMS (kitkat & google apps) on your phone as well. Otherwise you will not be able to get there.
* KitKat ROM (i9100) (CM11 M12 version) here
* Gapps (pico) here (set platform=ARM, android=4.4, variant=pico, and then press downloadbutton)
Reason for pico, is that I had trouble with the other (larger) versions. One kept crashing and the other wouldn't be installed (not enough memory). Don;t worry, you can install the google apps you are missing from the playstore later). I don't know if it was my phone related or samsung galaxy S2 related, so just go with pico to be sure.
Transfer all 3 files to your SD card on your phone.
STEP 4 - INSTALL new CWM
You now should have 3 files on your phone:
Time to first install the CWM. Note that this CWM is not compatible with the running OS so your phone will not be able to start correctly after installing, but this is OK, because right after we will be installing the correct OS (kitkat).
1) reboot your phone in restore mode. You can select the option in the current CWM app, or you can shutdown your phone and hold down Volume Up, Center Home, and Power buttons together for about 20 seconds.
2) Once in recovery, choose “install zip” for CWM browse your file system to install the ZIP file CWM-KitKatCompatible-i9100.zip
3) When done with installing go back in the menu to the 'advanced' menu and select "reboot in recovery". Or you can shutdown your phone and do it manually as in 1).
STEP 5 - INSTALL CM-11 ROM (kitkat) and Gapps (google apps)
1)With the previous step you should now be again in recovery mode. If not, go to recovery mode by
shutdown your phone and hold down Volume Up, Center Home, and Power buttons together for about 20 seconds.
2) go to 'advanced' and 'wipe dalvik cache' (confirm)
3) go to main menu and select 'wipe data/factory reset' (confirm)
4) select install ZIP and select the cm-11-20141115-SNAPSHOT-M12-i9100.zip
5) after installing again select install ZIP and select open_gapps-arm-4.4-pico-20160712.zip
6) after installing then select 'reboot system now'
STEP 6 - PUTTING BACK YOUR APP/SETTINGS BACKUP
Congratulations! Your phone is now running Kitkat. You may choose to first install Pokemon GO and check if it works ;)
You will see it is a clean install and you are missing all your apps/settings.
Download helium or titanium (whichever you used) and use restore.
Or if you are not happy with kitkat, you can do a restore via CWM restore to get your phone back to the state of Step 2. (but then you will not be able to play Pokemon GO).
One thing from my experience: it has a bug where the icons of the apps you moved to SD are disappearing from the homescreen. You may choose not to move your apps to SD (or at least the ones you want to have on your screen). Maybe the app 'link2sd' may help, but I haven't tested it yet.
To add pages, just tap and hold an app and hold it to the side of the screen.
As only gapps pico is installed, you may also want to reinstall google maps & youtube.
You will also see that your device storage has lots more space now that the unnecessary google apps are not there anymore (in my case hangouts etc).
STEP 7 - CATCH THEM ALL
Have fun :)
A powerbank may be needed on your journey as pokemon Go is a battery-lurker (with all models, not only the galaxy s2:) And enable battery saver from the pokemon go settings menu (screen will turn off when you hold the phone down).
NB: I'm not a phone expert, i'm just letting you know how I managed to get my samsung galaxy s2 working for Pokemon GO. Please do not ask me any technical questions.. but you may find fora/forums where you can ask your technical questions..