A while back, I bought some external battery packs to extend the battery life of my laptop. They're Energizer XP18000s. But I got the feeling that my laptop was going much slower with the battery connected. I just ran a build process as a rough benchmark to see how bad it is.
Plugged into external battery:
time make clean common real 8m7.359s user 46m23.586s sys 4m37.153s
Unplugged from everything: time make clean
common real 1m28.118s user 8m15.467s sys 0m55.539s
Any ideas why this might be the case, or how to improve the situation? If it matters, I'm running Windows 7 (time, make, etc. are running on an Ubuntu VM).