How to wire two 12v batteries in parallel

Written by david sandoval
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Watt's Law states that the power available in watts is equal to the electrical current (known as amperage, or simply amps) multipled by the voltage differential in an electric circuit. Batteries are commonly wired together to multiply one of these properties of electrical power. For example, wiring two 12-volt batteries in a series circuit will allow the circuit to operate at 24 volts, thus adding the two voltage differentials together. To increase the available electrical current, two batteries would be wired in a parallel circuit, where the voltage remains the same as each individual battery but more current is available.

Skill level:
Moderately Easy

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Things you need

  • Two 12V auto batteries
  • Electrical wire
  • Electrical pliers
  • Soldering iron and solder
  • Four battery terminal connectors
  • Two ring terminals

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  1. 1

    Cut two lengths of wire, and strip each end of each wire of 1/2 inch of insulation. Connect the first wire to one of the battery terminal connectors, and solder the wire to the battery terminal. Connect the other end of this wire and one end of the second wire jointly to a second battery terminal connector. Solder the wires to the battery terminal connector. Repeat this step to create a second battery cable with two terminals and one free wire end.

  2. 2

    On the free end of the first battery cable, install a ring terminal over the wire end, and solder the ring terminal to the wire. Install a ring terminal over the free end of the second battery cable, and solder the ring terminal to the wire.

  3. 3

    Connect the first battery terminal on the battery cable to the positive (+) battery post on the first battery. Connect the second battery terminal on this cable to the second battery's positive (+) post. Tighten the battery terminals on the positive posts.

  4. 4

    Connect the first terminal on the second battery cable to the negative (-) battery post on the first battery. Connect the second terminal to the second battery's negative (-) post. Tighten the battery terminals on the negative posts.

Tips and warnings

  • Ensure that both positive posts are electrically connected to each other, and both negative posts are connected to each other. If both batteries are connected improperly (positive to negative) to each other, both batteries will discharge quickly, overheat, and possibly explode.

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