Is it possible to purchase an external 72whr battery for a T470?

Hi there. I'm probably going to buy a T470, and it comes with the smaller 3 cell battery. However, if in the future I decide that I need a bigger battery, can I buy it from somewhere? I couldn't find a place that sold one...

EDIT: Got it in UK's ebay: http://www.ebay.co.uk/itm/11-25V-72Wh-Genuine-01AV428-Battery-for-Lenovo-ThinkPad-T470-SB10K97585-Series-/252824710055?hash=item3add86eba7:g:vN4AAOSwB-1Y0grU