I use my iPad 2 every day. I bought it in 2011, so it's basically 6 years old and battery is still in great quality. I disabled a few animations/transitions and such, and I run iOS 10. It's not as fast as it used to be (newer iOS not being optimized for slower iPads) but it's still perfectly usable for reading books on the Kindle app, some surfing etc. When I am not using it, I tend to put it in Airplane mode.
Also, the iPad 2 I got rid of like 4 years ago was horribly slow and pretty much useless at that point.