The Sony Xperia ZR (C550X) is one of the few premium Xperia handsets which has a removable battery. The Xperia ZR has a 2300mAh capacity battery, but if that is not enough for you then Mugen Power, extended battery specialists, has two batteries that will probably help.
The first is a 2500mAh extended battery (HLI-BA950SL) that will fit into the existing housing of the Xperia ZR and will set you back $44.50 with free delivery worldwide. The second is a 4600mAh battery (HLI-C5503XL), offering twice the capacity over the original battery and costs $89.50. This particular battery needs its own back cover, but Mugen Power offers these in all four colours of the handset (black, white, mint and pink). Both batteries will ship on 6 September 2013.