Always-on Mobile Data vs Background Data?

That's a good explanation above. Leave them all turned on and then to save battery just try to limit auto sync to the apps you really care about. When you want to save more battery the power widget lets you turn on/off auto sync really easily but be careful because every time you turn it back on it re-syncs all your programs and will use up a lot of juice if you turn it on/off a lot. When you REALLY need to save battery just turn off "mobile network" in quick settings. I've gone 3 days without charging like this and you still get calls and texts, just not 3g