UPDATE: Thanks to all who responded. I've found the perfect laptop to suit my needs.
The OP is below for archival purposes:
Hey guys and girls,
Looking for a new 13-15" Windows laptop around the $500 mark as I'm looking to sell off my Nexus 10 and don't want to be too far out of pocket. I originally had a laptop coming from Lenovo - but that didn't work out, as many of you know. So I would like to avoid Lenovo if at all possible, but if they turn out to be the best value, then I'll suck it up.
It will be used as a guiding computer for my telescope so long battery life is a must. Will not be used for gaming (as I have desktop for that) so GPU is completely unimportant. Looking for something with a decent 64-bit CPU. Windows 7 is greatly preferable as W8 generally sh*ts me to tears and I'm unsure of the compatibility with some of the astrophotography software I'll be using.
Thanks for any help you can give!
I can't recommend anything but of late there've been a number of tempting offers from MSY Technology. Maybe subscribe to their newsletter and wait it out?
http://www.msy.com.au/