Will Adding an Audio Amp Shorten a Car Battery's Life?

The addition of an automotive audio amplifier will not effect the life of the battery. The installation does, however, require some considerations as to the size of the amp and the worthiness of the electrical system as it stands. The battery serves three purposes: To start the engine, operate the electrical system in the event of an alternator failure for sufficient time to reach a service location and to operate the electrical systems with the engine off. Other than these situations, the battery is redundant since the alternator supplies all electrical power, including recharging the battery, when the engine is running.

Primary Considerations

The foremost consideration when including an amplifier in the stereo system is to do so without compromising the dependability of the electrical system. If the intent is to operate the stereo with the engine off, the battery reserve capacity is a consideration. This denotes the amount of amperage the battery will supply and for how long.

The next consideration is the alternator output rating in amps. The rating on an alternator is the maximum amperage its capable of delivering for a short period. Alternators should never be required to operate at peak amps for an extended period of time due to the heat generated through use. It is generally safe to maintain a 60 to 65 percent draw with the occasional flash to peak output.

Battery Selection

Your vehicle's current battery will suffice for operation of the stereo with the engine off, providing that the amplifier is not a high wattage unit over 400 watts RMS for short periods of time. For longer periods of operation using the battery alone, or if high wattage amps are used, a much higher RC rating for reserve capacity must be used. Twin batteries can be installed and isolated by a solenoid to avoid depletion of both batteries simultaneously. This way one battery can be used when the engine is off preserving the second battery for starting. This setup will extend the operational time of the audio system. Its a good idea to get a red- or yellow-top high-amperage battery.

Alternator Selection

To ensure your alternator will produce sufficient power to operate all the systems including the stereo amp, yet not exceed its safe output, its necessary to determine the normal vehicle draw versus the current alternator rating. The new amplifier wattage must be converted to amps and added to the original draw. If the total amperage draw exceeds the alternator output the battery will supply the difference foregoing the charging process. This is a recipe for disaster for the electrical system. It will run the battery down and overheat the alternator.

An easy method to determine the vehicles draw is to add the amperage rating on all the fuses, less for the starter fuse. This method will be good enough for this purpose however, it is not a truly accurate assessment since all the fuses are an average of 5 percent higher than the actual draw, and not all are in operation at the same time. It does give a quick reference for available amperage. Convert the wattage on the amplifier to amps. Wattage is power so amps (I) will equal wattage (P) divided by volts (V). For example: 400 watts divided by an average of 13.5 volts will equal 29.63 amps. Add the amplifier amps to the total vehicle system amperage for a total draw.

To preserve the battery and alternator, stay as close to 65 percent continuous draw as possible. The alternator will have a identification plate denoting its amperage rating.

Increase your output with a higher amperage alternator, if necessary, to save the battery and electrical system.

How to Reduce Audio System Draw

Voltage drop is a big problem with upgraded car audio systems. If the connectors have a loose connection, the ground connections are poor and the wire diameters are too small, voltage will drop from the front to the rear by as much as 1 to 2 volts or more. Using a 4-gauge or larger diameter cable from the negative post on the battery to the engine block ground location can provide a stronger system ground.

Always use soldered ends and make sure there is no paint between the ground location and the block, which can reduce or disrupt the connections ability to ground completely. All electrical connections must be soldered or have a good quality blade connector. Ensure that good ground straps from the engine to the frame are in place and ground the amplifier to the frame. The wire from the battery to the alternator or starter must have either a copper or gold plated connector.

If subwoofers are installed in excess of 6.5 inches, theire draw must be considered sincen they can create excessively high amperage draws when producing high-decibel bass notes. Watch the headlights when they are operating. Capacitors -- which have very low resistance and charge quickly to supply power for the subs without further stress on the alternator or battery -- may need to be installed, if the lights dim or flicker as the subwoofers hit.