umm, it cranks the motor right over for an instant start, i got it to chank my procharger more efficently for an instant start, even in the winter, and it holds more juice if your running a big stero, but i run my HID's right off the front terminal of the battery. =)
mine fit easy and its not as wide as the stock battery. the yellow top is what i got since its deep cycle and hold the charge good and holds up well with an audio system.