I've sort of answered my own earlier question regarding battery life on the II series by buying one.
Using 8 Eneloop batteries in my new MixPre-3 II, powering two Sennheiser 8040 mics, timecode switched off, recording just two ISO tracks at 32-bit float and I got just a couple of minutes over 5 hours.
"That'll do for me" I thought, since I use it for ambient recordings so rarely need more than an hour or two.
However, before selling my old MixPre-3 I thought I would repeat the test. Same setup, but with tracks at 24-bit, and I got just a few minutes short of 6 hours. Better than I imagined. I suspect this is because recording 32-bit float uses 20% more power, maybe I need to repeat the test at 24-bit on the II.
I've always been annoyed at the battery life of the MixPre-3, but never wanted the inconvenience of external power solutions. I suspect my annoyance has simply been a result of my own indiscipline, leaving batteries in the sled and finding they only last for a couple of hours when I pick it up.
(This is what I love about my Sony recorders. I can leave them in the car for months and they just work when I want to use them).
I am impressed with the 32-bit float. I will find it very useful for what I do, recording thunderstorms etc. I can happily report that 32-bit files work in Audacity.