How to Hook Up Two Batteries in an RV (Series & Parallel Connection Guide)

One of the biggest challenges RV owners face is making sure they have enough power while camping off-grid. Whether you’re boondocking in the desert or enjoying a quiet forest campsite, your RV batteries keep the lights on, the fridge cold, and the furnace running. But sometimes a single battery just isn’t enough.

That’s why many RVers choose to hook up two batteries. Doing this can give you more power, longer runtimes, and peace of mind when you’re far from shore power. But how exactly do you hook up two batteries in an RV? Should you connect them in series or in parallel? And what tools and precautions do you need to keep everything safe?

This complete guide will walk you step by step through the process. By the end, you’ll know exactly how to wire two RV batteries the right way and avoid common mistakes.

1. Understanding RV Battery Basics

Before you start wiring, it helps to know the basics of RV batteries.

1. RVs typically use two types of batteries: chassis batteries (for starting the engine) and house batteries (for running appliances). In this guide, we’re focusing on house batteries.
2. Most RV house systems run on 12 volts DC. Some RVers use two 6V batteries in series to make 12V, while others connect two 12V batteries in parallel to increase capacity.
3. Battery capacity is measured in amp-hours (Ah). The higher the amp-hour rating, the longer your batteries can power devices before needing a recharge.

2. Why Hook Up Two Batteries in an RV?

There are several benefits to using two batteries instead of just one:

1. More capacity – A dual battery setup lets you store more energy, meaning longer off-grid stays.
2. Better reliability – If one battery fails, you still have a backup.
3. Supports bigger loads – Appliances like fridges, furnaces, or inverters need higher power, which two batteries can handle better.
4. Flexibility – You can choose between series and parallel wiring depending on your needs.

3. Series vs. Parallel Connections Explained

When hooking up two RV batteries, you have two main wiring options: series or parallel.

Series Connection (Best for 6V Batteries)

1. Increases voltage by combining two lower-voltage batteries.
2. For example, two 6V batteries wired in series = one 12V battery bank.
3. Amp-hour capacity stays the same as one battery.
4. Ideal if you’re using 6V golf cart batteries.

Parallel Connection (Best for 12V Batteries)

1. Voltage stays the same (12V).
2. Capacity doubles – two 12V 100Ah batteries = 12V 200Ah system.
3. Great for RVers who want longer battery runtime.
4. Works well for boondocking and solar charging setups.

Key Difference

• Series = higher voltage.
• Parallel = higher capacity.

4. Tools & Materials You’ll Need

Before starting, gather these essentials:

1. Two matching RV batteries (same type, age, and size).
2. Heavy-duty battery cables (2/0 AWG or 4 AWG depending on system size).
3. Wrenches and screwdrivers.
4. A battery tray or box to hold them securely.
5. Protective gloves and goggles.
6. Multimeter to check voltage.
7. Optional: battery isolator or disconnect switch.

5. Safety Precautions Before Hooking Up Batteries

Working with electricity always carries risks. Stay safe with these steps:

1. Park your RV on a flat, stable surface.
2. Turn off all appliances and disconnect from shore power or generator.
3. Wear gloves and safety glasses to avoid acid burns or sparks.
4. Never mix old and new batteries, or different types (AGM, flooded, lithium).
5. Double-check polarity before making any connections.

6. Step-by-Step: Hooking Up Two Batteries in Series

This method is mainly used for two 6V batteries to make 12V.

1. Place the two 6V batteries side by side in your RV battery box.
2. Connect the positive terminal of Battery 1 to the negative terminal of Battery 2 using a heavy-duty cable.
3. Connect the RV’s positive lead to the free positive terminal of Battery 2.
4. Connect the RV’s negative lead to the free negative terminal of Battery 1.
5. Test with a multimeter – you should now read 12V output.

Result: Voltage doubles (6V + 6V = 12V), but capacity remains the same.

7. Step-by-Step: Hooking Up Two Batteries in Parallel

This method is common when using two 12V batteries.

1. Place both 12V batteries side by side in your battery box.
2. Connect the positive terminal of Battery 1 to the positive terminal of Battery 2.
3. Connect the negative terminal of Battery 1 to the negative terminal of Battery 2.
4. Connect the RV’s positive lead to one battery’s positive terminal.
5. Connect the RV’s negative lead to one battery’s negative terminal.
6. Test with a multimeter – voltage should remain 12V.

Result: Voltage stays the same, but amp-hour capacity doubles.

8. Common Mistakes to Avoid

Many RVers make wiring errors that can damage batteries. Avoid these pitfalls:

1. Mixing different battery types (AGM + flooded, or lithium + lead-acid).
2. Wiring series when you need parallel, or vice versa.
3. Using cables that are too thin, which can overheat.
4. Forgetting to secure the batteries in place.
5. Not installing fuses or breakers for safety.

9. Maintenance Tips for Dual Battery Systems

To keep your dual batteries working well:

1. Inspect battery terminals regularly for corrosion.
2. Keep batteries clean and dry.
3. For flooded batteries, check water levels and top up with distilled water.
4. Use a smart charger or solar charge controller for balanced charging.
5. Fully recharge after each use to prevent sulfation.

10. Real-World Examples: Series vs. Parallel

Different RVers use setups depending on their needs:

1. Boondockers with solar – prefer parallel 12V batteries for more storage.
2. Weekend campers – often fine with one battery, but two in parallel gives longer stays.
3. Full-time RVers – may use large lithium banks in parallel for maximum runtime.
4. Golf cart battery fans – use 6V batteries wired in series for durability.

11. FAQs

1. Can I connect a 6V and 12V battery together?
   No, never mix different voltages. It can cause damage.
2. Do both batteries need to be the same age?
   Yes. Mixing old and new reduces efficiency and lifespan.
3. Can I charge both batteries at the same time?
   Yes. In both series and parallel setups, the charger will charge both batteries.
4. Which is better for RVs, series or parallel?
   If using 6V batteries, series is required. If using 12V batteries, parallel is best for more capacity.
5. Can I run my RV air conditioner with two batteries?
   Not for long. You’ll need shore power or a generator for heavy loads.

12. Conclusion

Hooking up two batteries in your RV is one of the best ways to extend your off-grid adventures. Whether you choose a series connection for 6V batteries or a parallel connection for 12V batteries, the process is straightforward with the right tools and safety steps.

Always use matching batteries, check your connections carefully, and maintain your setup regularly. With a properly wired dual battery system, you’ll enjoy longer camping trips, more reliable power, and the freedom to explore without worrying about running out of energy.