I'm using ThinkPad E520 with dual graphic card: ati and intel.
I usually get 5-6 hrs battery life in windows with GPU auto switch on.

Since i'm now using linux, I disabled discrete card in BIOS,
and now `lspci` do not show anything about my ati card.

But, the problem is, I can just get about 2 hrs of battery life in linux, i think the ati card is still sucking power, how do you guys think? what should i do?

big thanks!