Google Play updates on mobile connection despite setting Even though I have set the option not to update apps on mobile connection, it still updates them and Google Play app is the number one in my mobile connection usage. How to fix it?
AFAIR that setting is only applied to apps installed thereafter, so you've got to disable it for each app separately in addition. I've made that back then right when the autoupdate feature was introduced, so I don't remember anymore where exactly this has to be done (Playstore app or playstore website).

Doing a little Google Search brings up e.g. this article: How to Disable Automatic App Updates on Android, which in short describes the required procedure as follows:


Globally disable/enable auto-updates (applies as default to apps installed after changing this setting):


Open the Google Playstore app
Head to Menu→Settings
Toogle the Auto-Update Apps setting to the wanted value

Adjust it for apps already installed:


Open the Google Playstore app
Head to the list of your installed apps ("My Apps")
Open each app separately, hit the Menu again, and toggle the Auto-Update checkbox

Restricting Google Play to WiFi: (also see my answer here, with screenshots)


From your homescreen, go to Settings→Data Usage
Enable a "global limit" (can be pretty fake, e.g. "5 TB" – it just needs any value, which one doesn't matter for this case)
In the list of apps below, scroll to the Google Play Store app
Open its entry, scroll to the end of the page
tick the checkbox to "restrict background data"



Above order (1 &amp; 2) applies to "I want auto-updates globally, just not for certain apps". If I understood correctly, the "Auto-Update" checkbox on the apps' pages only becomes visible when auto-updates are enabled globally. So if you want to deactivate that for all apps, you might have to reverse this order:


Enable auto-updates globally
Disable it for each installed app separately
Disable it again in the global settings (so it will automatically be applied to apps you install from now on)


Not very user-friendly, especially with many apps installed – but it at least should work.

Item #3 will stop Google Play Store from working while on mobile data. While usually, this just affects background data, Play Store will most likely refuse to work altogether, as it relies on GCM (Google Cloud Messaging), which relies on background data to receive messages.



More references:


How to stop Google Play Store from auto updating (YouTube video)
How can I turn off the “allow automatic updating” for all apps? (right here on Android.SE)
Is it possible to disable Google Play updates? (specifically for Google Play and Google Play Services, which – according to the answer there – can not be excluded from auto-updates)
How can I turn off the “allow automatic updating” for an app? (again right here on Android.SE)
How to enable Play Store auto-update for just a few apps? (one more here on Android.SE)
Is it possible to selectively limit background data usage?
How does “Restrict background data” work?


There are many more links, not all fitting in this answer :)