I found out a few months ago my battery was dead. It still started the car just fine but if I left anything on for more than 10 minutes without the car running I would need a jump.

So after my credit card came in I got a new battery from walmart. To my surprise my mpg increased from 26-28. Not great but every little bit counts. Just thought I would give everyone else the heads up to get their battery checked, it can affect more than you think.