1 From what I can see on the web the highest capacity 18650 battery available is ~3500mAh, AFAIK there are no genuine 9900 or 15000 products (despite what the label might say)

What do you mean "genuine" ? A battery is a battery. I can't figure out what a "genuine" battery is.

The one I'm using currently is branded GTF, 9900 mAh. It has been in the XHDATA for three times the duration the original 2200 mAh battery was capable of, and it's still alive... and kicking... ;)