Maybe you want to consider a beefy desktop with a battery-backup and plugging it in someplace cold and setting up a laptop to remote into it. You can get a lot of bang for your buck in a desktop, and going lean on the laptop means you don't need to compromise on cpu memory or storage. They even make special video cards that do the remote desktop encoding (PcOIP) that are really quite fine for coding, but I find xpra to be just fine for me.