Batteries are a pain, expensive, large and too heavy. Like Barry I use a small genset (honda Eu10i) which has 1kv capacity clean power (excellent for laptops, garanteed better than mains) and will run for 8 hours on 2L of unleaded. Quiet as a mouse (52dB) and as light as a feather (~15kg wet). Best thing is it is about the size of a shoe box so takes up little space. It even has a special circuit to charge 12V batteries built in. A much better option then deep cycle batteries by a fair margin. Runs my mount, CCD's, laptop etc etc at idle. Details here.
http://www.hondagenerators.com.au/in...id=12&Itemid=2
Mark