I was stumbling around eBay and found this little addition to my E6520. It's a genuine Dell External Battery. It is compatible with a lot of Dell units. It is kinda cool in that it elevates my E6520 up off of surfaces so it should help with cooling it better. It only snap/plugs into the expansion slot and the two holes adjacent to the slot. It has a small handle on it that you can pull to release the battery from its mating position. I believe the two holes in the upper left corner of the picture are first, charge indicator and then a charging port so you could possibly charge the external battery by its self.
They range anywhere from 60 to 140 dollars depending on new or refurbished condition.
I also noticed that my battery indicator in the status bar seems to be working now. I can even see the current percentage of charge. Im happier.