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What Size are Marine Battery Posts/Terminals?

size of marine battery terminals

Whether you’re using a trolling motor or outboard engine, a marine battery is critical to ensuring your boat runs smoothly in the waters.

If you’re new to marine batteries, the process of finding the right terminals for replacement can be quite complicated. There are a number of reasons you may be looking to replace battery terminals. 

Sometimes it’s a problem with the vehicle’s existing wiring, while other times, it’s an issue with the battery itself. Perhaps the terminals have been damaged, corroded, or not delivering the connections you need. 

We’re here to simplify what deep cycle battery terminals are and what sizes you’ll need for your battery. 

Let’s get started! 

What Are Marine Battery Terminals?

marine battery terminals

Marine battery terminals are electrical contacts used to connect your charger to the deep cycle battery. 

These terminals typically have dual posts; a positive and negative threaded post along with a pair of SAE tapered posts. 

Marine battery terminals are made from heavy-duty annealed tinned copper to provide maximum current flow. 

Additionally, 100% tinned plated copper posts are constructed to resist corrosion from moisture and salt. 

A properly crimped battery terminal that features adhesive lined shrink tubing seals out any moisture, the battery cables, and battery remain dry and corrosion-free. 

Worn or corroded battery terminals could be the source of battery or engine problems. Bad terminals lead to poor connections, resulting in a heavy electrical arc that destroys the battery post. 

If the marine battery is outgassing, the arc could cause the battery to explode.

Furthermore, never use temporary terminals for permanent use. They tend to corrode and fail quickly, meaning they should only be used for emergency use. 

Always replace the terminal if you notice any signs of wearing. 

What Size Terminals Are on Deep Cycle Batteries?

Renogy Deep Cycle AGM Battery 12 Volt 100Ah

Marine batteries usually consist of two posts. The negative terminal is measured at 5/16″-18, while the positive terminal is measured at 3/8″-16. 

Are Car Battery Posts the Same Size?

Interstate Batteries Automotive Battery 12V 63Ah

The size of car battery posts can vary in size. Side post car battery terminals are the same size as deep cycle terminals, but other car battery terminals are typically larger. 

Like marine batteries, side post car battery terminals have two recessed female threads that are 3/8″. These posts must be attached to battery terminal adapters. 

Other car battery posts will usually come in 10 mm, 11 mm, or 13 mm. These sizes aren’t the same as deep cycle batteries when converted to inches. 

What Are the Sizes of Other Battery Posts? 

WindyNation Marine Grade Battery Terminal Top Post Kit

Here’s a table comparing the sizes of various battery terminals. This gives you an idea of which terminals can be used based on your battery cables. 

Types of Battery Terminals  Size
Auto Post Terminal (SAE Terminal) Positive post – 17.5 mm
Negative post – 15.9 mm 
Stud Terminal 3/8” 
Marine Terminal (Dual Post Terminal) Positive Post – 3/8”  

Negative post – 5/16” 

Button Terminal 8 mm 
AT Terminal (Dual SAE/Stud Type Terminals) 3/8” 

Below, we’ll discuss common battery terminals and how they can be used: 

Auto Post Terminal (SAE Terminal): Auto post terminals are typically used for most car batteries. Anybody who has replaced a car battery will probably recognize it. 

Stud Terminal: These terminals are designed to easily fasten and secure the terminal connection to the lug and lead base of the terminal. 

Marine Terminal (Dual Post Terminal): A marine terminal features an automotive post and a stud terminal. The connection can be made using a ring terminal and wing nut or traditional pressure contact. 

Button Terminal (Insert Terminal): These terminals are between M5 to M8. This refers to the metric size of the bolt thread’s diameter. The button terminals are frequently used for AGM batteries .

AT Terminal (Dual SAE/Stud Type Terminals): These terminals are frequently used on traction-type batteries for heavy cycling applications. This type of terminal has an automotive post and stud like the marine terminals. 

Connecting Battery Terminals 

How to Replace Battery Terminal Connectors Made Easy!

Whether you’re using a marine battery terminal or a car battery post, make sure to use a proper terminal lug  that matches the size of your battery cables. 

Then connect the battery cables to their terminals.

Next, attach this assembly to the battery.

When installing the battery terminals and cables, it’s recommended to use only high-quality crimping and stripping tools.

Replacing Boat Batteries 

How To: Replace a Boat Battery

When you’re replacing your boat batteries, you’ll need to clean and connect the terminals properly. 

Follow the steps below to replace your old marine battery with a new one.

  1. Open the boat’s battery compartment and examine the condition of the battery terminals.
  2. Gently clean any acid leaks and buildup of toxins around the terminal. If corroded, you’ll need to replace the terminal and follow the steps above. 
  3. Remove the negative and positive terminal using a plier  or wrench . Never use your hands to loosen them. 
  4. Carefully remove the old boat battery. 
  5. Properly place the new marine battery  in the battery compartment.
  6. Connect the positive cable terminal to the battery’s positive post. Then tighten the stainless steel nut. 
  7. Connect the negative cable terminal to the negative battery post. Tighten the nut. 

Proper Maintenance and Care for Marine Battery Terminals

10pcs Battery Terminal Anti Corrosion Washers

Boat batteries can suffer from performance issues, which poor battery cable connections may cause. 

Under tightening, overtightening, and corrosion can occur over time. That’s why it’s important to check the connections periodically to see that the connections are secure and tightened.

Always refer to the battery manufacturer’s recommendations for proper connection and maintenance. Depending on the type of terminals used, you’ll need the proper lock washers and stainless steel nuts. 

Most terminals will require you to position the lock washer between the connector and the nut. Then apply the recommended torque to compress the lock washer without damaging the lead terminal. 

Battery terminals should be cleaned regularly using a wire brush  and a cleaning solution of  and water. This helps to neutralize any residue of electrolytes that may be left on the surface. 

Never apply lubricants or grease between the connectors and terminals, since it disrupts the connection. 

Always examine the cables to see if they show any signs of corrosion or damage. Try giving the cable a good tug to see if the connections are weak. 

Any indication of corrosion, melted insulation, or acid leaks means you should replace the terminal. 


Marine battery terminals are designed to resist corrosion and provide a secure connection to the batteries. 

This ensures you’re receiving maximum energy capacity and a great performance from your battery. 

As a result, you can enjoy boating or fishing for a long time without worrying about battery failures or poor connections. 

Now you’re ready to replace your battery terminals and get out in the waters!