now, I'm no expert (and there is no end of websites run by battery experts), but there is a limitation as to how many mah can fit into a certain space.
That is, the OEM battery size gives a certain output, and you can probably get a bit more in the same form factor.
But not double

Simply don't believe the bullshit out there. Whether it's chinese, japanese, gold or silver.
Older teminal designs allowed manufacturers to market physically bigger batteries with a custom cover, of course that is not an option here.
I am quite happy as long as I can get a day out of the phone, charging overnight.
If you want a 11,000 mah battery, look here:
http://www.amazon.co.uk/Largest-Capacity-In-The-World+1-AMP-Faster-Charging/dp/B004CHMP50/
There you go, your phone will run forever with that baby hooked up to it.
I bought a 5000 mah pack for about 2/3 the price, mainly since I want to be using the gps for tracking (and being tracked) purposes while out in the country on my mountain bike. Works very well, it's not heavy, it's a bit like having another small phone with you