I use a BH VLF/TR, 707, 505 and a Quickdraw II and I get about 25-30 hours IF I always use my headphones.
Then again I only use MAHA POWEREX 9.6 Volt 230mAh NiMH Rechargeable Batteries. I have found through experience that these batteries are true workhorses.
The good thing about this is that these are true 9 volt batteries and not the 8.4 or 7 volt that most rechargeable's are.
I really hate to buy batteries and a couple sets of these charged up leave me worry free.
By the way these batteries do NOT develop any charge memory. I also get more time by switching around the batteries in the detector after about 10 or 15 hours because one battery always drains faster.
Its also handy when you take those treasure trips to the boonies, I just use the charger in the Jeep.