There are mainly two methods to wire a second car battery. These two methods include the parallel method and the series method.

Parallel method

This method maintains the endurance of the battery but will double the battery’s voltage. To wire the second car battery using the parallel method, this is how you go about it.

  1. Using a wrench, you need to cut off the two battery cables from the car.
  2. Put the second battery next to the existing battery. Connect the cables from both the existing and the new battery to the negative point of the current battery.
  3. Connect the second and the existing battery cable to the positive (+) point of the original battery. When you have done this, ensure that the cables do not come in contact or touch the car.
  4. Join the end of the cable (of the latest one) attached to the negative zone of the present one to the negative zone, the second battery.
  5. After the car ignites, reconnect the cable of the original battery joined to the negative (-) of the existing battery of the car detached in step number one.
  6. Now you need to join the new battery cable to the negative area of the second battery to the car disconnected in step number one.

Series method

This method maintains the endurance of the battery but the voltage is doubled. This method is usually not recommended, and you should only connect using this method if you are sure that your car’s voltage is equal to voltage of both batteries combined.

If your car’s voltage is less, you will damage the electrical system of your car. In addition, the fuses will blow. To connect your car using the series method, you should follow the following steps.

  1. Disconnect the battery cable from your car.
  2. Ensure that your car is set to use 24 volts (this is the voltage of two batteries)
  3. Connect the cable of the new battery to the negative terminal of the already existing one. Now, connect the other end of the cable to the positive connector.
  4. Attach the cable of the original battery to the negative terminal of the second battery, and reconnect the cable of the battery to the positive unit of the existing battery.