You have described the phones well, your first GZ is the first version, was told there were several bugs in it.  The second one is like mine.  I still have not found a place to find a second battery, I like to charge one and just replace them, therefore no downtime.  Since I have three phones, that is possible, but the local store still does not handle batteries.  the charger is made like my old LG that I liked, you can charge a battery separate without a phone.  I seldom turn mine off, if I don't get a lot of calls it will last almost a week, heavy use about three days, depending on your definition of heavy use. 

From my experience with you for three days 24-7 last year, and how you use your phones, the battery might last a half-day for you?  (Grin)