I did a little experiment with my optimus black to see how long would battery last with minimum use. About my config:
I'm on Zeus 6.22 with JuiceDefender Ultimate. I configured a lot with JuiceDefender e.g. nightmode which automatically switches to airplane mode, sync is handled by JuiceDefender every 2 hours, wlan only, only 2G, auto display brightness (power saving). I did some calls and wrote some messages (normal and whatsapp), didn't play any game.
So far so good. The result was amazing: I was on battery for 6 days and had about 16% battery left!!! Look at the screen capture.