The first charge takes the longest, which is probably in that eight hour range. I haven't ran the Anker dead yet. I usually charge it back up after I used it, so it's fully changed whether dead or just a little. But it's a few hours.
The tablet takes about three hours or so from completely dead, assuming it's off. You can charge the tablet back up on the Anker.
I don't know about much on the electricity. I'm sure the tablet has a regulator of some sort, but couldn't say if 16v in would fit with in it or not.
There other larger battery packs like Anker. The problem is most don't have a way to put out the amps needed to register a charge for the tablet. Most just have USB ports, and limit the output to the normal .5mha that work with 90% or other usb devices.