I upgraded my iPad and iPhone 5 to iOS 6.1.3 last week and both devices had huge battery drain issues. The most noticeable was my iPad which seemed like it was dropping 15% of battery charge per hour just watching a movie on my flight from NYC to SEA. My iPhone was having the same problems.
I read the forums and many were seeing the problems and it looks like the forums are making more noise. Enough to have CNET post an article.
My fix which seems to work is I turned off e-mail fetching completely. Not push. Not every 15,30 min or hour. Sync mail manually. I only retrieve e-mail when I choose to sync. And, my battery now lasts a lot longer. I liked it so much I turned off regular e-mail retrieval on my Samsung Galaxy Note as well.
Living without the constant stream of e-mail took a bit to get used to, but I actually like it better now.