Regular car batteries are designed to give a high amp short burst output (to start the car) then be charged back up again. Leisure batteries are designed to give a lower output over a much longer time, often draining the battery down before it gets recharged.
Whilst a car battery will happily do the job we ask, it simply wont last very long (which matters not if you get them for free from the local tip). That is why I'd recommend a designated leisure battery.
__________________
|