How long can a battery last?

Last January 16, I bough a Nikon D5000 + Sigma 70-300mm. I have 4GB SD card, and one battery.

If I were to shot RAW + Jpeg Fine, how many shots can I make with just one battery? I'm asking this because I'm thinking of a buying another SD Card in preparation for Dinagyang Festival this Saturday and Sunday. I can't afford to buy another battery so, if my current battery can only last for a 4GB, I will not buy another SD Card.

This is Dinagyang

14 groups are participating this year, which will last between 8:00am to 1:00pm… After that, there will be street dancing until 12:00 midnight.

Buy more batteries. Period!

Its an open ended question, there's no definitive answer, how long do you take between shots? Are you using flash? Do you turn the camera off between locations or when having lunch? Can you turn the rear screen off (these take loads of current)? All these, and more effect how long the battery will last, the size of the memory card makes no difference.

When photographing events my battery usually lasts all day, but I always take a couple of fully charged spares just in case.

One thing I will say is that new Li-ion batteries don't get to full charge until they have had a few charge/discharge cycles. Then they slowly loose capacity from that high level over time (years).

See page 231 in your manual fro information about battery life. Just for "average use" you can see that you should get around 500 shots. This is regardless of what size or quality the image is. Next, you need to calculate how many RAW + JPG Fine images will fit on a 4GB card. Look on page 215 of your manual and you will see that a 4gb card will hold approximately 180 such images. This means that you could easily fill your 4GB card on one charge and you are likely to be able to fill two 4GB cards. If you use an external flash, you will get more shots, because the battery will not be used up firing your pop-up flash.