I didn't see anything definite but 'm pretty sure that it's an internal battery. But here is the other info you asked about.
Storage: 2GB internal (approximately 1.4GB available for user content).
Content Formats Supported: Kindle (AZW), TXT, Audible (formats 4, Audible Enhanced (AAX)), MP3, unprotected MOBI, PRC natively; PDF, HTML, DOC, JPEG, GIF, PNG, BMP through conversion.
Kindle makes it easy to take your personal documents with you, eliminating the need to print. Each Kindle has a unique and customizable e-mail address. You can set your unique email address on your Manage Your Kindle page. This allows you and your approved contacts to e-mail Word, PDF documents, and pictures wirelessly to your Kindle for a small per document fee--currently only 10¢ per document. Kindle supports wireless delivery of unprotected Microsoft Word, PDF, HTML, TXT, JPEG, GIF, PNG, BMP, PRC and MOBI files.
You can email your PDFs wirelessly to your Kindle. Due to PDF's fixed layout format, some complex PDF files may not format correctly on your Kindle.
If you are not in a wireless area or would like to avoid the fee, you can send attachments to "name"@free.kindle.com to be converted and e-mailed to your computer at the e-mail address associated with your Amazon.com account login. You can then transfer the document to your Kindle using your USB connection. For example, if your Kindle email address is Jay@Kindle.com, send your attachments to Jay@free.kindle.com.