Just ordered another one on the OCUK weekly deal. Already have the SSD waiting for it
In some way you doubled your battery life.
I just discovered that OCUK is a kind of a store or a commercial web site. ^^
I watch at the weekly deal for the MSI X600 and I saw that they cheated the battery life as it is said to be 8 hours with a 6 cell battery !

That's simply impossible !!!
So here is the result of my second test of battery life, but only partial test : as it was again an Internet and Office use and I forgot to switch bluetooth off, so only light was reduce to 50% ==> 3.45 h !
Almost 50 mn gain reducing the light by 50% and again with the standard 5400RPM HDD. Not bad...
If you are interessed here is a link for a 9 cell battery :
http://www.buy-laptop-battery.co.uk/msi-laptop-battery/msi-btym69-battery.html
You may surely find cheaper elsewhere, but do not buy a model to be said a 8 cell battery (4400 mAh) you can find in some other web sites as the power is less than the basic 6 cell battery (5400 mAh).
I hope I can find a cheap capacitive touch panel so I would modify this X600 as I am so accustomed with my Acer 1825PTZ with it's touchscreen that most of the time, I use to touch the panel trying to scroll the web pages...

Even the touchpad is not that good compared to the Acer or the Asus one for page scrolling. :/