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How to Charge Two 12 Volt Batteries in Parallel

How to Successfully Charge Two 12 Volt Batteries in Parallel

Connecting and charging two 12-volt batteries in parallel is a practical solution for many who require extended battery life and increased capacity without altering the voltage. This setup is ideal for applications such as RVs, marine vehicles, and solar power systems, where maintaining a constant voltage while doubling the capacity is essential. This guide provides a step-by-step approach to safely charge two 12-volt batteries in parallel and highlights the benefits of choosing Himax Electronics for your battery needs.

Understanding Parallel Charging

Parallel charging involves connecting two batteries together so that their capacities add up, but the voltage remains the same. Here’s why and how this is beneficial:

  • Increased Capacity: By connecting two batteries in parallel, you effectively double the amp-hour (Ah) capacity, allowing your system to run longer between charges.
  • Redundancy: This setup provides a backup; if one battery fails, the system can still operate on the other battery.
  • Uniform Voltage: The voltage remains consistent with a single battery, ensuring that devices or applications connected to the battery bank operate within their voltage specifications.

Tools and Materials Needed

To connect and charge your batteries successfully, you’ll need:

  • Two identical 12-volt batteries
  • High-quality battery cables
  • Suitable connectors for secure connections
  • A wrench set for tightening connections
  • A reliable battery charger compatible with your battery type

Step-by-Step Guide to Charging in Parallel

  1. Prepare the Batteries:
  • Ensure both batteries have similar capacities, states of charge, and are of the same type. This uniformity is critical to prevent imbalances that can lead to undercharging or overcharging.
  1. Connecting the Batteries:
  • Connect the positive terminal of the first battery to the positive terminal of the second battery using a high-quality cable.
  • Connect the negative terminal of the first battery to the negative terminal of the second battery using another cable.
  • Secure all connections tightly to ensure there is no loose contact, which can lead to sparks or poor charging.
  1. Attach the Charger:
  • Connect the charger’s positive lead to the positive terminal of one of the batteries.
  • Connect the charger’s negative lead to the negative terminal of the other battery.
  • Ensure the charger is appropriate for the combined capacity of the batteries.
  1. Begin the Charging Process:
  • Turn on the charger once all connections have been checked and secured.
  • Monitor the charging process closely, especially if it’s the first time you are charging these batteries in parallel.
  1. Monitoring and Maintenance:
  • Regularly check the voltage of each battery using a multimeter to ensure they are charging evenly.
  • Inspect the battery terminals and cables periodically for signs of corrosion or damage, which could affect performance.

Safety Tips

  • Always wear protective gear, such as gloves and safety glasses, when working with batteries.
  • Ensure the area is well-ventilated, particularly when charging lead-acid batteries.
  • Never leave the charging process unattended for extended periods, especially in new setups.

Why Choose Himax Electronics?

Opting for Himax Electronics for your battery and accessory needs brings several key advantages:

  • Reliability and Efficiency: Himax Electronics offers products that are tested for reliability and efficiency, ensuring that your battery setup performs optimally under various conditions.
  • Expert Advice: With years of experience in the battery industry, our experts can provide tailored advice on battery selection, charging strategies, and maintenance practices.
  • Quality Customer Service: We pride ourselves on exceptional customer service, offering support and guidance through every step of your battery setup and maintenance process.


Charging two 12-volt batteries in parallel is an excellent way to increase the capacity and reliability of your power supply without upgrading to a higher voltage system. By following the detailed steps provided and adhering to safety protocols, you can ensure a successful setup that meets your energy needs. For all your battery needs, consider Himax Electronics, where innovation meets quality and customer satisfaction is a priority.