Do you need a Second Battery for Car Audio?

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Who needs a second battery?

Whether you need a second battery for car audio is determined by your application and by how much power your amplifiers are using. 

Is this a daily driver for work commutes, grocery runs, and nights out on the town?

Is this a nasty, ground-pounding, Sound Pressure Level record-shattering beast?

Last week, we covered High Output Alternators, following the Big Three Wiring Upgrade. 

If you’re following along, you’ve done the Big Three Wiring Upgrade and added a High Output Alternator. 

Are your headlights still dimming? 

If headlight dimming still happens when the system plays heavy bass notes, your amplifiers are drawing more power than your charging system can create. 

Headlight dimming is a cause for concern. Underpowering your amplifier can lead to overheating, clipping, and the red light of despair known as the protection light.

Your stock electrical charging system was designed and built for the stock features of your car. 

The stock battery was made to start the engine. 

The stock alternator was designed to charge your batt and power the stock electrical components in your car.

Adding high draw amplifiers to the mix increases the load that your electrical system requires to operate.  

Your alternator provides amperage to your system. 

When your system is trying to use more power than what is available, your gear will go into protect mode or worse.  

Adding a high output alt reduces the strain on your charging system.

If you want to demo and enjoy music at high volumes for extended periods, you’ll need a second battery.

Secondary batteries are necessary when running the car stereo for extended periods of time. 

Secondary batteries are also a necessary addition for systems with such a large power draw, and systems where the electrical needs exceed the output of the alternator.

If your concern is listening to music, you can easily calculate the current needs of your stereo. 

To estimate the listening life of your battery or determine how much charging power your second battery should have, use the following equation. 

10 X (Battery capacity in Amp Hours) / (Load Power in Watts) = Running time in hours.

If your batt has a 75 AH rating, and your amplifier draws 1,000 Watts, that would be calculated as:

10 x 75 / 1000 = .75

With 75 Amp Hours and 1000 Watts of amplifier load power, we would be able to listen to music for about 45 minutes.

If your desire for music listening time is greater than the current your electrical charging system can provide, you’ll need to add additional batteries.

Do you still need a secondary battery even if you don’t plan on giving demos at car shows?

That depends on how much power your amplifier is using. For systems using 1500 watts or more, headlight dimming should be alleviated by adding a secondary battery.

You can figure out the amperage draw of your system using Ohm’s Law to determine how much capacity you’ll need.

I (current) = P (power in wattage) divided by E (power in voltage)

Let’s say you’ve got one 2,000 watt amp like the q1-2200.2 and a 1,000 watt multiple channel amplifier like the Q4-150. 

That’s 3,000 watts. Your alternator is rated at 14.4 volts. Now that we know what two of the three values are, we can solve for the third value

3,000 watts divided by 14.4 volts = 208.3 amps. 

You’ll still need enough amperage to operate the electrical components in your car or truck like fans, windows, ignition, and power steering. 

Most electrical systems need between 60-120 amps to operate, so let’s factor that in too.

3,000 / 14.4= 208 + 120 = 328. For this system, you’d want 328 amp hours of charging power available.

About Batteries

There are two primary chemistries used for batteries: Lead-Acid and Lithium. 

Within these categories, there are a multitude of variations, including AGM, sealed lead-acid, LTO, and many more. 

These all have specific advantages in their uses. 

Sealed Lead Acid Batteries (AKA your grandpa’s batts) are inexpensive.

SLA batteries have low rates of self-discharge and perform well in low and high temperature environments. 

Traditional SLA starter batteries are also heavy and have a low weight to energy ratio. 

Furthermore, they have a limited cycle life and are very slow to charge.

Absorbed Glass Mat (AGM) batteries improve over traditional lead-acid designs with a glass mat separator to wick the electrolyte solution between plates. 

The glass mat has enough charge for the battery to deliver its full capacity. 

AGM’s can be very heavy compared to contemporary options, like lithium. 

They improve on SLA batteries in terms of available charge, charging time, and cost. 

AGM batteries are maintenance free and reliable, but there is a dropoff in available voltage as they deplete. 

Lithium batteries are more expensive than traditional SLA and AGM batteries. 

There are a few reasons for this. 

Lithium batteries have about 45% of the weight of AGM batteries. 

Lithium batteries charge faster than AGM can. Lithium is also capable of delivering 95% of the capacity without a significant change in voltage until the cells are drained. 

Next time, we will cover wiring practices to get the most out of your secondary battery!