What is a Capacitor Battery?

Dave Slovak

A capacitor, or capacitor battery, is similar to a regular battery in that it stores an electric charge but also very different in its design, composition, and purpose. In particular, a capacitor has a lower energy density and charges and discharges more quickly. Many people use capacitors in addition to batteries to enhance an electrical system and increase the lifetime of the battery.

Many cars use a battery along with a capacitor battery to lengthen the life of the battery.
Many cars use a battery along with a capacitor battery to lengthen the life of the battery.

Most cars, boats, airplanes, and other automobiles utilize a complex electrical system that connects various instruments and components, from the vehicle’s exterior lights to its interior lights, indicators, heating and cooling systems, and any audio systems that may be installed in the automobile. All of these components are part of a system that is powered by the vehicle's battery system. The battery is most likely continuously charged by the vehicle’s alternator while the vehicle is running.

A drained car battery can be started by attaching jumper cables to the battery of another car with a charged battery.
A drained car battery can be started by attaching jumper cables to the battery of another car with a charged battery.

When an electrical system produces frequent, heavy load on a battery, both the battery and the electrical components can suffer negative effects. For example, a car audio system that uses an amplifier will require a large charge to power the speakers, particularly those that use high-voltage amplifiers to create loud bass notes. Every time the speaker produces a sound, the amplifier draws heavily on the car’s battery. As a result of the battery discharging frequently, the car’s alternator has to recharge the battery more quickly than it normally would. In fact, most factory-installed alternators are not designed for this type of frequent battery recharging.

In the long run, this type of activity reduces the life of the alternator and battery. In addition, the audio system components may suffer. If the amplifier high electrical resistance, the system’s wires can become hot and the speakers or other components may short-circuit or blow a fuse.

Car audio experts know that to avoid these types of problems, individuals can install a capacitor battery. When installed properly, a capacitor battery can provide the quick discharge of electrical current without harming the battery. The capacitor battery quickly charges and discharges electricity based on its design. Instead of transferring electrons, a capacitor stores the charge using two plates: a positively-charged plate and a negatively-charged plate. A material called a dielectric resides between the two plates, and the positive and negative charges remain balanced on either side of the dielectric.

A capacitor battery is designed to absorb the peaks and valleys of voltage produced by a system. The positive and negative plates maintain proportional charge so that when a system requires quick, heavy load, the capacitor provides the electrical current. When the system needs to remove electricity, the capacitor can quickly store it and avoid disrupting the circuit.

In addition to applications within car audio systems, there are other uses of capacitor batteries. For instance, many vehicles with regenerative braking mechanisms use a capacitor battery to store the resulting charge. This usage is prevalent in electric and hybrid vehicles. Certain transportation industries require the use of a capacitor battery in vehicles in order to extend battery life to reduce costs and environmental impact.

Using an amplifier draws heavily on a car's battery.
Using an amplifier draws heavily on a car's battery.

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Discussion Comments


@Terrificli -- That problem was all on the stereo installer. Did the mechanic know about your big old subwoofer? Should that mechanic have known the electrical problems it could cause?

I don't know the answer to either of those questions but I do know that someone who installs stereos for a living should know how to install a stereo so it won't fry your electrical system.

The stereo shops that don't install things right usually aren't around for long, so I suppose you'd better take up your complaints with them before they are gone.


Great. I had a subwoofer installed a few years ago and that must have been the reason why my alternator and battery became problematic after those things were put in. The stereo shop never mentioned a thing about a subwoofer potentially ruining my battery and alternator.

I wonder why a mechanic didn't pick up on what was causing my problems when my car we being serviced?

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