On my tf300t ASUS tablet (with wifi only) I tried to set "Restrict Background Data" following

Settings->Data Usage->three boxes in the upper right corner,

but there is no such option. I read on some forums that this option is only available with limited mobile data, but the option to set a limit is not available under Settings->Data Usage->three boxes in the upper right corner.

There is, however, an option under

Settings ->Developer Options -> Background process limit,

but I'm not sure about it. On my Gingerbread phone, background processes were disabled, and whenever I wanted to download an app, I had to enable it. With the Backround Process limit, however, downloading is possible (therefore, I'm not sure if this is the equivalent to Gingerbread's setting). Furthermore, I noticed that, after setting Background Process limit, every once in a while I get a message that some Asus process has been terminated. My question is: how would one disable background processes (no connections to wifi while screen off, ...) in order to save the battery?