The batteries found in conventional cars and in hybrid cars are both rechargeable. The difference is in the construction of the battery’s interior and the amount of energy the battery can store.

The Conventional Car Battery: The Key to Starting Up

The lead acid battery in a conventional car contains enough energy to drive a small electric motor. It is “gear reduced” to generate enough torque to turn over a car engine at about 300 RPMs to start the engine. A burst of energy is needed for a short period of time to do this.

During the winter when the oil is thick and parts are tight, it requires a lot of current from the battery to turn over the engine. Some engines require as much as 600 amps of current to turn over the engine. That’s why, when buying a car battery, one is concerned with the "cold cranking current rating." These batteries are designed to deliver a burst of current for a short period of time. Otherwise, the battery is only needed to support accessories such as the radio, lighting, security system, power windows, power locks, and entertainment systems while the engine is not running.

When the engine is running, the alternator supports all the required electrical demands of the vehicle. It also charges the battery back to its full potential so it will be ready to turn over the engine for your next start-up.

The automotive battery is designed to always be ready, willing, and fully charged—to discharge a lot of energy for starting the engine. Running this type of battery until it’s fully discharged would quickly kill the battery’s ability to store energy in the future.

The Rechargeable Hybrid Car Battery

A hybrid car uses a conventional lead acid battery for all the same reasons that a conventional car uses one. But a hybrid car also has a rechargeable battery, which is constructed quite differently. It is what is called a deep cycle battery. The internal construction of the battery allows it to be fully discharged and recharged over and over again. It is very similar to a battery used in electric vehicles such as GM’s EV1 or a golf cart or new-fangled electric personal scooters. The difference is that electric vehicles need a lot of stored energy, since the stored electrical energy is the only fuel the vehicle has to make it move down the road.

These batteries are very large and heavy. For an example, the battery pack in the Electric Ranger battery build by Ford in the late 1990s was 1600 pounds. These batteries carried a serious amount of energy. Most of these battery packs are a series of smaller batteries connected together in a series array that adds up to a higher voltage.

The hybrid car uses a mixture of today’s gasoline engine and the battery found in electric vehicles (EV), which found little acceptance in the passenger car market. The hybrid battery has evolved a generation or two since the EV days. Today Nickel-Metal-Hydride (NiMH) is being used for hybrid batteries instead of lead acid to reduce the weight and deliver more energy from a smaller package. Because a hybrid also uses a gas engine, the size of the battery is not as large as a pure electric vehicle EV battery. On vehicles such as the Honda Civic and Insight, and the Toyota Prius, the hybrid battery voltages are 300 volts or greater. Where the starter battery in a typical car was measured by cranking amps, hybrid batteries are measured by kilowatt-amp-hours.