The Micro Four Thirds format has many advantages over ‘traditional’ DSLRs; unfortunately battery life is not one of them. I own an Olympus E-PL2 and Panasonic G3, both of which have never seen the better side of 350 photos on a single charge.
When you consider that a) OEM batteries cost the best part of £50, and b) even an enthusiastic amateur motorsport photographer can take 1000 photos at a single event, all of a sudden that £400 camera you bought isn’t looking too cheap if you want to use it for a good length of time away from electricity. I personally pack 3 batteries for a single day motorsport event.
Thankfully there are alternatives, most Micro Four Thirds cameras happily accept third party batteries that can cost as little as £10. Things are a little hit and miss though, some do not show the battery life indicator, and some just flat out refuse to work, you can also wave goodbye to your warranty if it causes a problem. Check out a friendly M43 community such as MU43 User Group to find out what works and what doesn’t.