The Sony Xperia V (LT25i) is thankfully one of the high-end Xperia phones that comes with a removable battery. The original BA800 battery has a capacity of 1700mAh (minimum), similar to that of the Sony Xperia S (LT26i). If you are planning on buying a spare for your water & dust resistant Xperia V, then you may want to consider the Mugen Power alternative.
Mugen Power, extended battery specialists, have a 1800mAh extended battery that will offer a modest increase over the stock battery for $46.95 with free shipping worldwide. This battery will fit happily into the existing enclosure no need for a separate door either. The item appears to be in stock but ships on 11 January 2013 for those that are interested.