Can i run TWO battery saver/booster apps on my andriod phone at once?

I just got the htc EVO 4G and i didn't get the extended battery, so i downloaded DROIDFUEL and JUICE DEFENDER, two apps that are supposed to boost battery life.. anyways, can i run them both at the same time and save even more battery or is that just pointless. oh and one more thing, what is task killing? i dont understand that, im new to andriod phones. thanks guys.