Got the battery and a charger today.
The battery is a Hyperion 3S 20-30C 800mAh, and when I put it on the scales I got a nice surprise. It only weighed 68grams - 70 with the connector from the old battery - so I'm shaving 13 grams off of the total weight of the X-UFO. That, and I'm doubling the power... That translates into FLIGHT TIME!
I got the battery and charger from Elefun.no, a Norwegian shop, but most well-stocked R/C-hobby stores, particularly those catering to 'electric-flight' enthusiasts, have them in stock.