Cheap Dual Battery Setup

Introduction

Want a simple and inexpensive way to add a second battery to your Ford Ranger or Bronco II? This setup uses a basic isolator solenoid to allow both batteries to charge while the engine is running, while keeping your starting battery protected when the engine is off.

When wired correctly, this system lets you run accessories from a second battery without worrying about draining the battery needed to start your vehicle.

NOTE: This setup will NOT work properly on 2019 and newer Ford Rangers due to their smart alternator systems.

Things You’ll Need

• Two batteries (similar type and size recommended)
• 60 Amp circuit breaker (one for each battery) – Circuit Breaker
• ANL fuses and fuse holders (one for each battery if you don’t want to use a circuit breaker) – ANL Fuse & Holder
• Battery cables (4–6 gauge recommended) – Battery Cables
• Battery lugs – Battery Lugs
• Battery terminals – Battery Terminals
• 12-gauge wire (for solenoid trigger) – 12 Gauge Wire
• 4-gauge wire – 4 Gauge Wire
• Battery isolator relay (solenoid)
  • Stinger 200 Amp Battery Solenoid
  • PAC PAC-500 500-Amp Battery Solenoid

How This Setup Works

This system uses a solenoid (relay) as a switch between the two batteries:

• Key ON / Engine Running: The solenoid closes and connects both batteries so they charge together.
• Key OFF: The solenoid opens and separates the batteries so your accessories cannot drain the starting battery.

The circuit breakers or fuses protect both batteries and wiring from shorts.

Diagram & Installation

Follow the diagram carefully. The wiring path matters.

Step-by-Step Instructions

1. Mount the second battery
   Choose a secure location and make sure the battery is properly fastened.
2. Run power from the starting battery
   Connect a short 4–6 gauge cable from the positive (+) terminal of the starting battery to a circuit breaker or fuse.
3. Connect to the solenoid (input side)
   Run a 4–6 gauge cable from the circuit breaker to one large terminal on the solenoid.
4. Run power to the second battery
   From the other large terminal on the solenoid, run a 4–6 gauge cable to a second circuit breaker or fuse.
5. Connect to the auxiliary battery
   Run a short 4–6 gauge cable from that circuit breaker to the positive (+) terminal of the second battery.
6. Connect the grounds
   Run a 4–6 gauge cable from the negative (-) terminal of the starting battery to the negative (-) terminal of the second battery.
7. Wire the solenoid trigger
   Connect a 12-gauge wire from the small terminal on the solenoid to a fuse in your fuse box that is only powered when the key is in the ON position.

Important Notes

• Install a fuse or circuit breaker as close to each battery as possible
• Use 4–6 gauge cable for proper current handling
• Keep cable runs as short as possible
• Use batteries of similar type and age for best performance
• Make sure all grounds are clean and secure

Related Articles

Dual Battery Setups

Adding An Auxiliary Battery To A 2019+ Newer Ford Ranger

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Auxiliary Electrical Systems

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Last Updated: April 16, 2026