The adapter is basically a USB Plug/Socket with a couple of resistors on the inside to emulate the correct voltages on the D+/D- lines. When in use, the Nook HD sees my batteries as AC input. I picked mine up on eBay for around $5 from a seller in CA. DealExtreme has one that is slightly different but should work the same. dx.com/p/usb-2-0-male-to-female-extension-cable-w-data-charger-switch-for-samsung-p7510-more-black-258964
Here is the listing on eBay for the one that I bought. ebay.com/itm/190702898352?ssPageName=STRK:MEWNX:IT&_trksid=p398 4.m1497.l2649
This will possibly help many like myself who have batteries already that the Nook HD/HD+ just doesn't like.
Hope it helps!!