Battery life on the Amazon Kindle Fire HDX 8.9 is excellent. Amazon promises up to 10 hours of mixed use, but that figure is really meaningless because mixed use is different for everyone.
In our testing, it averaged anywhere between 7-10 hours of use, which included some games, streaming TV shows, checking e-mail and browsing the web. By today's standards, we'd say the battery held up rather well.
If you plan on giving this thing extensive use on a daily basis, which is a little hard to imagine, you may need to charge it every day. Otherwise, every other day will be just fine.
What the Kindle Fire HDX 8.9 has over the 7-inch model is a rear camera. It's OK, but not great. In low-light situations, instead of increasing ISO or sensor sensitivity, the shutter speed drops rather dramatically. This results in more blurry images.
Color reproduction is also OK, but not the greatest, and images tend to look noisy and oversharpened, too. We'd compare the images produced by the 8MP rear camera to those being taken by smartphones about three or four years ago.
Surprisingly, if you can hold it perfectly still, HDR works nicely. Light and dark areas of your scene will have good detail, and there is little to no halo effect on edges, which is nice.
In the end, we wouldn't run around with the Kindle Fire HDX 8.9 taking pictures all day, but we suppose it's nice to have in a pinch or if you're using it to record or broadcast video.