How can I change the battary of my pmp jdx661?

I would expect it to last a lot longer than you say.
Read on about sales description.

The two words 'Up to ' can be confusing. The description of sales of this model 'Up to' 150mins of high resolution video using the built in 1GB card or 'up to' 400mins if a 2GB SD card is plugged in.
Now that can significantly reduce in time if fliming continuous. My camera if I film continuous looses power quicker than stop, start filming. So it could be you are using it to much too long expecting the same power lasting results as above.

However being a new one I also advise you take it back to the store of purchase and get them to check it out.

Nobby
March 2009