how to pick a 2nd battery?

[steve volz]

looking to get a new 2nd battery. how do you find what size is good for the power you are running? im planing on maby 3000 rms at the most.

[BEEMDUB]

this might help a little bit

Determining the current capabilities of your vehicle.

Before installing a power amplifier in your system you should take into consideration the vehicle’s ability to provide adequate current to the amplifier. In most vehicles, the alternator is only capable of supplying a little over the requirements for the standard electrical system (i.e. headlights, air conditioning, etc.).

How you play your system will determine the amount of current you will need. For example if you listen to your system at low listening levels, then you’ll probably use less than one-third the rated current draw. If you play your system loud, then you will use most of the rated current of the amplifier.

Most alternators have about a 40 percent reserve capability. In order to determine how many in amperes of current you will have for your system; you will need to find out alternator rating. If you’re not sure of the total amperage of your alternator, a good place to look is on the alternator itself. Most alternators have a metal tag stating the total average available. If you can’t find the tag, check with the manufacture to find out the rated amperage. Once rated current of the alternator is determined, you need to multiply this number by .40 in order to determine the reserve current available for use with your power amplifier.

For Example:

Alternator = 80 Amps 80 x .40 = 32 Amps

Please keep in mind this is an estimate only and not exact science. It is best to get your electrical system tested by a professional to determine the electrical system's true capabilities.

Calculating amplifier Current Demands

By using the fuse value of the amplifier you can get a rough idea of the amount of current draw that will be used under full output power. Although the full output rating is good to determine the total amperage draw in the system, it does not represent the true continuous or averaged amperage draw in the system. Listed below is a simple way to determine the approximate continuous current draw of your amplifier.

1.) Determine fuse value of the amplifier.

2.) Divide the RMS power Rating by the Peak power rating.

Example:

50Watts RMS Divided by 100 Watts Peak Power = .50 (50%)

Once you figure the percentage of RMS vs. Peak power, you multiply the fuse value of the amplifier by the RMS percentage.

Example:

If the amplifiers fuse value was 30A, then 30A multiplied by 50% would be 15A of continuous current draw.

Upgrading your Electrical System

Depending on systems current requirements vs. your electrical systemss capabilities, you may need to upgrade your electrical system. For example, if you find that your headlights dim when you have your system cranked up at night, this is a sign you should upgrade your electrical system.

There are several different ways to accomplish this. One way is to upgrade the alternator so that it has higher amperage output.