Using Auto Proxy Discovery lowers Battery life

I've recently signed up to my college's WiFi - one of the things I had to do to connect was to enable 'Auto Proxy Discovery'. At home where this option isn't needed, I get around 6-7 hours of just general web browsing from my battery. At college, I am lucky to get 2.5. BatteryTimeRemaining is showing that I am using roughly 30W which is significantly higher than I normally do at home - however, I can also see that my CPU usage is only around 6-12% meaning nothing CPU intensive is going in the background - what's going on? I don't particularly want to have to bring my charger with me to college but I can't do with only 2.5 hours of battery life!