Replaced mine a few weeks back whilst the wagon was in the garage, from memory cost me about £15 each (looking at the bill, but that will be with labour on top) not that bad a job to do just couldn't be bothered to do myself. John (the garage man) connected them in turn to one of those starter/booster packs to check operation 2 x dead, 1 x slow, 1 x ok. if your going to check them like he did be very carefull they get very hot very quickly.
in my case it didn't cure the poor starting either, to date: new fuel lift pump, new battery, assorted fuel lines, new sedimenter, filter and it still takes at least 7 turns of the engine before it fires up in the morning or when being left for more than a few hours!