Aspire 4720z battery issue

Lately, my Acer 4720z's battery has been draining in about 2 hours as opposed to the 3+ hours it used to last. During the summer, for about two months, I didn't use the laptop at all and in my infinite wisdom I forgot to take the battery out during that period. I'm suspecting that was the culprit. Only having a 2 hour battery life is a problem at school because I don't always have the time to recharge my battery between classes. What I'm wondering is if there is any way to improve the battery life, or if the damage done is permanent (I'd really like to avoid buying another battery).