I'm looking for a Laptop to use as a "Thin Client"

I have remote desktop enabled on my main PC (2 Licences) and would like to have a laptop that connects to it for around the house/out and about use. 
This way I have access to all my files and software, without the trouble of installing the stuff I need again or copying files to usb. 

So far its turned out to be an awesome idea, and have been using an old Dell to test, but its heavy and the battery lasts 2hrs at best.

So, what I need is a light laptop with a long battery life. Ideally built-in 3G/4G so I don't have to tether my phone while travelling.

What would you suggest?

Thanks,