I have 4-7mA idle consumption screen down depending on I don't know what. Idle battery life is ca. 8 days. It reports 15days if after charging the usage is 4mA, but it likely won't stay so low. I've done some measurements with powertop, but can't really pinpoint the cause of variation.

When the phone is under normal use I recharge it every night or every other night.

You can also get some battery information with bmestat from command line. If you want that info when device is idle you can add some delay before the command, make it execute on background and even write output to the ramdisk (though i suppose it's useless as the result is written after the measurement.)
-> close the terminal and idle the device. After 60 seconds passed you can open the terminal again and...
Btw. I don't think the Battery Usage app uses much power unless you are keeping it's UI open (you can close it, budaemon monitors in the background).