That's an interesting question.
My biggest issue with the battery life of my ZX1 is how much runtime is lost to the Ether. Letting it sit in "sleep" mode—even with a whole host of services disabled, all push/pull notifications turned off, and all radios silenced—I lose, by my calculations, approximately 5.5% battery capacity per 24 hours.
I typically find myself charging it once every 4-5 days. And realistically, I've only listened to 12-14 hours worth of music during that time. Said music is comprised of a majority of MP3s and a relatively small contingent of FLAC 16/44.1 CD rips. No sound enhancements enabled other than the 5-band EQ.
I've installed Wakelock Detector to try to figure out what's causing the drain. Best I can figure, it's Alarm Manager. But even with hundreds of "wakes" it still only results in a couple of minutes worth of run time over the course of a few days. It doesn't seem like that should be responsible for a 5.5% drain per day.
The only logical solution I can come up with is to buy a ZX2.