Given that it is second hand and it could be quite old, it's very possible that the battery is not all that good any longer.
My suggestion is to replace the battery. Here is a link to a very good site to order the battery. They give you the tools you need and they also have an instructional video on how to replace the battery.
http://www.newpower99.com/B_N_NOOK_S...mple-touch.htm