If you've just purchase your first RV or boat, you'll need to know a few things about deep cycle batteries. Let's start by answering your first question: What is a deep cycle battery, and how is it different from a car battery? A car battery provides a short burst of energy to get the motor running, then the alternator takes over to provide the electrical power for the car as you drive. Since a car battery only provides the initial surge of electrical current, it doesn't drain much juice from the battery with each use. On the other hand, a deep cycle battery will use the majority of the battery's energy with each use. With an RV or boat, you need a lot of steady power; a deep cycle battery provides it.