What is the Watt-hour rating of the lithium-ion battery in the third generation iPad?

See this page and look for your model number to get information:

https://www.apple.com/legal/more-resources/docs/apple-product-information-sheet.pdf

That's not a published specification on the Apple Website, so we wouldn't know as this is a user to user only forum. You can reach out to Apple directly to see if anyone can answer your question. Either call Apple or use the Contact Support button at the top of this page.

Thanks Roger, I've never seen that before and will remember it in case anyone else asks.