I have a Lumia 820 for 2.5 years now. The battery usually lasts for only one day even without using it. I recognized that the battery lasts significantly longer (three up to five days) when I'm in a different country. I guess it's connected to the fact that I don't have any data connection via 3G/LTE when I'm not in my country (Germany). But even when I turn off data connection and turn on battery saver when I'm home the battery is still being fully discharged after a maximum of two days.
Can anybody explain that behaviour? Does anybody know a solution?