I have to agree, Pandora *is* designed for a (very) long standby.
I own two and I didn't timed them but they didn't empty quickly at all.
the battery is a huge (as wide as the device itself) 4000 mAh.

I easily keep my pandoras in standby mode for a week.

I'm looking forward to know how long a Neo900 and a Pyra will be able to last in standby/use.