How to Set Up a Second Battery in the Trunk for Car Audio

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How to Set Up a Second Battery in the Trunk for Car Audio
An auxillery battery just might save you from needing a jump start. (dead battery image by Katrina Miller from

The high-power amplifiers and bass boosters of today's car stereos make listening to the music feel more like attending a concert. The speakers are powered by huge amplifiers and crossover boxes designed to maximise performance and sound, and many of the higher-end stereo systems even incorporate high-energy capacitors to store energy, which enable the extreme amounts of bass to reverberate and be heard for several city blocks. All of this power drainage is tough on a charging system, and many people install high-output alternators in their cars. The really smart people add an auxiliary battery.

Skill level:

Things you need

  • Wrench
  • Drill motor
  • Drill bit
  • Wire cutters
  • Wire
  • Wire stripper
  • Terminal ends
  • Battery box
  • Battery
  • Ground cable
  • Self-tapping screw
  • Screwdriver bit for the drill motor

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  1. 1

    Park your vehicle. Turn the engine off. Open the bonnet and disconnect your vehicle's battery by removing the negative terminal connection with a wrench. Open your boot.

  2. 2

    Decide on the location for the second battery. In most systems, the area right beside the amplifiers in the boot is the best and safest location. This also puts the new battery in close proximity to the stereo components, making the wiring a bit easier. If your amplifiers are mounted in a location other than the boot, you could mount the battery in close proximity or simply route the wiring from the boot-mounted battery to the amplifiers. Space will dictate the location of your new battery.

  3. 3

    Mount the battery. Locate the battery box where you want it in the vehicle. Place a drill bit into the drill motor and drill through the battery box's mounting tabs and into the boot floor. Using the hardware that came with the battery box, place a bolt through each of the mounting tabs on the box and the holes you drilled. Tighten them with a wrench.

  4. 4

    Wire the battery positive side. Using a heavy gauge copper wire of at least 2 gauge, run a piece of wire from the positive side of the new battery to the power lug of the closest amplifier. Using a wire stripper, remove just enough of the cable's protective plastic coating to allow you to crimp a terminal end to each end of the cable (wire). Attach one end to the positive terminal post on the battery and the other to the power lug of the amplifier. Tighten the connections with a wrench.

  5. 5

    Run a ground cable from the negative side of the new battery to the floor of the boot. Tighten the battery clamp with a wrench and secure the other end to the boot floor by inserting a large self-tapping screw through the cable eyelet and screwing it tightly to the boot floor with a screwdriver bit mounted in a drill motor. Reconnect the vehicle's original battery ground cable and tighten it with a wrench. Close the bonnet and boot.

Tips and warnings

  • Remove the ground wire when disabling a battery. This will prevent dangerous sparks from burning you.
  • Never work on a battery system unless the ground has been removed. Failure to do so could end up shorting out the entire electrical system.

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