I'm just curious how many of you have purchased extra (spare) batteries for your laptop computers to have on-hand 'just in case'. I don't have one (yet) because I use mine primarily at home and have easy access to an AC outlet, but I may want to use it away from modern conveniences someday. According to ebay, I can purchase a spare for $50-$75 plus ~$20 shipping. I'm just not certain I really need one. Recommendations?