Nissan Tiida 2008: Why won't it start?

Every now and then my 2008 Nissan Tiida has problems starting. It will crank, but won't actually start. My local Nissan dealer said that it is the calcium battery that they say tells the starter motor not to start the car if the volts are below a certain level. They recharged the battery using a surge charger, but it still won't start at certain times. Is it the battery or is the immobiliser just not disengaging when I turn the key? It cranks so I don't think the battery is at fault. Would a new battery fix the problem?