fdr1968

I have a 2008 Prius with 83,000 miles. My battery has died twice; once because I left an interior light on and a jump start fixed the situation. Next time, about 1 month later, nothing was left on, and on start up all the indicator lights came on and I couldn't get my key out. A second jump start solved the problem. My concerns: I had the batttery tested at the dealer and they told me it was fine. I have a warranty on the battery to 100K. Interestingly, my MPG have been steadily declining from a high of 48 on purchase to 43 currently. My driving has no changed. The MPG have gone as low as 40 recently. I am wondering if I am not getting a straight answer from the dealer about the battery? Anything else that might affect my MPG? Thanks-