When you're driving and headlights start to dim because a high-powered stereo is cranking, that means the deep bass you hear is causing total vehicle electrical draw to exceed the rate at which your alternator can charge the battery. Ask any audio expert about this and they'll tell you the same thing - a high-end system needs its own battery source!
Because low voltage conditions can confuse engine management computers and will cause a host of related issues, we've got audio power cells that eliminate this problem. Installed in sequence with a primary battery, audio power cells provide a reserve of power from which to draw. In this article, we'll refer to them as "second batteries".
We caution that reserve power provided by a second battery won't last indefinitely unless you install a higher-output performance alternator. It's unlikely you'll be cranking your amps at full blast every second you're in the car - but if you plan to, headlights will eventually dim again because your standard alternator still can't charge both batteries any faster than normal. Bear in mind also that keeping a second battery charged means extra work for an alternator, often overtaxing worn-out ones.
Another benefit of a second battery is that it creates an additional reserve of power that extends the time you can play your stereo with the engine off. If this is your main objective, it might be a good idea to put a battery isolator between the two batteries. This ensures amplifier power is drawn only from the secondary battery, not the primary one used to start the engine.
Understanding Electrical Power
When looking at batteries, you'll see numerical ratings for wattage and Voltage. Watts is a total measure of power that's based on several factors inherent to electricity. First, voltage (V) is a measure of electrical force (think water pressure in a pipe). Power cells we offer match the standard 12-volt strength of automotive electrical systems.
Current (amps) is the flow rate of the electricity (think of the speed at which water can flow through a pipe). Electrical flow rate can be increased by thicker wiring (akin to a wider pipe) and by further reducing electrical resistance that impedes the flow (removing hardened gunk from the pipe).
Total power (wattage) is a measure of voltage multiplied by current (amps). We've got power cells ranging from 400 watts up to 4,000.
AMP-HOURS: How Long a Battery Will Last With The Engine Off
Battery reserve capacity (RC) is important to consider if you plan on using your stereo or anything else without the engine running. There's a formula for calculating how much time you have for this - but first, you'll need to know the electrical draw of your amplifier/system in watts (known as "Load"). Assuming the battery is at full charge, the formula is:
(10 x Reserve Capacity) divided by Load = hours of Operating Time (known as "amp-hours").
If your stereo pulls a 250 watt load during operation and your battery provides an RC of 80, the formula equates to: (10 x 80) / 250 = 3.2 amp-hours. So you have 3.2 hours before this battery drains below engine cranking point. Weaker battery condition and colder temperatures can reduce real world amp-hour performance.
A second battery can be installed in the engine bay close to the primary battery or in the trunk near an amplifier. If your vehicle already has a rear-mounted battery, you won't need to run a power cable from front to back. Here, we'll look at a simple installation where the primary battery, secondary battery, and amp are all in the trunk. If you're not completely comfortable with running a cable from front to rear through firewalls and the interior of your vehicle, we recommend professional installation.
For this job, you'll need battery cable lugs, a length of battery cable (at least 2/0 gauge thick), wire cutter, and assorted hand tools. You'll be making 4 separate new connections including the amplifier connections. Cut your cable wire into 4 sections (measure twice, cut once) before attaching a lug to each of the ends. As always, it's important to use a matching gauge thickness for all power and ground cables.
If you'll need to anchor the battery to something solid, we recommend a battery box (see our Shuriken product page) that serves as a mounting bracket while encasing the battery.
1) First, disconnect the negative (-) cable from your primary battery. ALWAYS remove the negative cable first, so as to avoid any potential short-circuits when handling the positive (+) battery cable. Then disconnect the positive (+) battery cable.
2) Run power between the 1st to 2nd battery by connecting one lug of your first new cable (wire shown in blue in the above picture) around the bolt used to tighten the primary battery (+) clamp. Connect the other end of the cable to the (+) post of the 2nd battery.
3) On top of the (+) connection you just made at the 2nd battery, stack another cable onto the same (+) post and run it to the amp.
4) Create a ground for the 2nd battery by running the third new cable section you created from the (-) battery post to an unpainted metal point on the vehicle. Do not use the same grounding spot as the primary battery.
5) Create a ground for the amp by running your fourth new cable section from the (-) amp connection to a different unpainted metal point on the vehicle.
Reconnect your primary battery by first connecting the positive (+) cable, and then the negative cable. We've also got additional battery cables and connectors should you need to further customize your connections.
As you can see, a second or auxiliary battery can solve a host of issues if your ride is chock full of high-end audio or other electronic goodies. Installation is straight-forward - doable by yourself if you're handy, and reasonable if you need to hire it out. Check out the options and crank those tunes!