You may want to contact Sony's Laredo Service Center, which did the prs-500 update.
Phone: 1-866-357-6230
Email:
SonySVCLRD@am.sony.com
Last time I called I was told nobody had reported the battery problem to them yet. But they did agree to send me a UPS lable to get the 500 back to them. My reader is in their center right now. Not sure if they could fix it though. Check the thread
here for repair update.