Motorcycle Battery Terminals 101

Motorcycle Battery Terminals 101

In my experience as a Harley-Davidson Master Technician, some of the most common issues I have seen is from people installing batteries themselves.  This is actually an easy job, but it is just as easy to mess up. The biggest issues normally center around the battery terminals. I will do my best to break this down and explain the issues and why.

First let me start by saying, Harley-Davidson makes a great battery.  All Harley-Davidsons run an AGM (Absorbed Glass Mat) battery. This means that they are maintenance free.  There is no need to check the water or electrolite levels. All you really need to do is keep it charged. NEVER PUT A LEAD-ACID BATTERY IN YOUR MOTORCYCLE. 

This is what happens when you install a battery cable on a terminal incorrectly.

What is different about a Harley-Davidson Battery?

Long story short, H-D batteries have a Patented battery terminal setup. This proprietary design allows for direct connection of the battery cable to the battery terminal, with no adapters or spacers. EVERY other battery on the market uses some type of spacer or adapter. This is the first and foremost reason for sticking with an H-D battery on your H-D bike. See some examples below

Harley-Davidson battery terminal

A Harley-Davidson AGM Battery has terminals that are flush with the outside of the battery case. This allows the cable to attach directly to the terminals with no spacers or adapters.

All other batteries have in-set battery terminals that are not flush with the outside of the case. This is important as these batteries will require proper screws and spacers.

MANY NEWER BIKES AND SOME OLDER BIKES USE THE TOP OF THE BATTERY FOR CONNECTIONS. THESE BIKES DO NOT NEED SPECIAL SCREWS OR SPACERS.

How do I know I have it installed properly?

Most battery manufacturers provide a new screw and spacer with a new battery. In most cases the spacer is a brass color. This is where most people go wrong and they do not realize that they need it. They have a flat spot on them and that should be facing down against the battery case. This is demonstrated below.

The proper position for the battery terminal spacer

This is a proper installation of a screw with cable and spacer on the terminal.

What’s the big deal? It’s just a spacer right?!

While “just a spacer” may be true, it is the most important component in the whole setup. When you make a an electrical connection, you need to make sure it is a good connection. A battery cable that is not sitting flat against the terminal will create an air gap between the cable and the terminal. This allows the electricity to “arc” across this air gap. This “arc” that is created creates a lot of heat. A loose battery terminal or an improperly installed battery terminal will create heat and can melt the terminal right off of the battery.

THIS IS NOT THE RIGHT WAY TO CONNECT THE CABLE!!!

Note the lack of a spacer on this battery connection! This is a perfect example of what happens when not installed correctly.

What should I do to prepare?

I will almost always give the same answer to this no matter how complex the job. Get a Factory Service Manual. Not a Clymer’s or any other brand than the OEM that makes your motorcycle. Those manuals will always give you the specific information that you need. If you cannot afford $100 for a manual (just shooting a fairly high number out there), don’t work on your own bike. As a professional technician for many years I have tens of thousands of dollars in tools and I myself will not work on anything without access to a factory service manual. Over the years I have bought more than I can count. Mostly digital as paper copies can get damaged or lost so easy. I have not only bought them for my motorcycles but all of my 4 wheeled vehicles as well. They are resources that are only valuable when you need them. But when you do, they are well worth the money.

4 comments on “Motorcycle Battery Terminals 101

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