A lot depends on:
How bright the lamps have to be?
How big is the battery?
Let us assume that you have a car battery, nominal 12 volts.
If that is so, then don't use 2.4volt lamps, use 12 volt lamps.
Looking at the website you gave, they have 12v lamps of the type you want in 1.2W, 2W, 2.2W, 3W, 5W and 6Watt rating.
If you want maximum battery life then use the 1.2W lamps.
If you want maximum brightness then use the 6Watt lamps.
So, what size battery have you got, how many lamps do you want and how bright do you want the lamps?
JimB