Motorcycle Battery Charging Basics

The first step when testing electrical problems or systems is to test the motorcycle’s battery. A fully charged and properly functioning battery will serve as a base line for diagnosing other electrically related problems. This article will help you identify what type of battery you have, how to measure its state of charge, and how to keep it charged and in optimum working condition.

Identify your type of battery:

First you need to determine what type of battery your motorcycle has. There are two basic types of batteries—Flooded and AGM.

• Flooded batteries can be identified by the removable caps located on top of their cases.  These batteries may require filling as the water level drops.  Only use distilled water when filling a flooded battery.
  

  Typical flooded 12 volt motorcycle battery

• AGM (Absorbed Glass Mat – also called Maintenance-Free (MF)) batteries have no removable caps and are permanently sealed after activation.  These batteries do not require filling—ever.
  

  Typical 12 volt AGM motorcycle battery

Find out what type of battery your motorcycle should use by going to the Yuasa website, and selecting the year, make and model of your particular bike.  Some motorcycles can use either type of battery while older bikes can only use flooded batteries.

Measuring the battery’s state of charge:

To determine the level of charge for your battery, a measure called “Open Circuit Voltage” is required.  This is the voltage your battery has when not under any electrical loads.  You must first remove any static charge that the battery might have.  This is accomplished by placing an electrical load on the battery.  You can simply turn on the ignition switch for about 2 minutes, then turn it off and let the battery rest for about 10 minutes.  Then connect a Digital Multimeter directly to the battery and read the voltage.  If you are not familiar with how to use this tool, read our article: Basic Digital Multimeter Operation.

Now refer to the chart “Battery Open Circuit Voltage” below.  Make sure that you are reading the values for the type of battery you are testing.  The reading on the Digital Multimeter will correspond with the amount of charge that the battery has. If it’s less than 75% the battery needs to be charged before load testing. NOTE: Load testing your motorcycle battery will give you an accurate indication of how it will perform during vehicle operation. Read Motorcycle Battery Testing to learn how to load test your battery. The open circuit voltage test will not provide enough information to determine if the battery is good—only how much charge it has.

Use this chart to determine the level of charge of your battery

Charging your battery:

Ideally a motorcycle, or power sports specific battery charger should be used for charging.  These “Smart” chargers will not damage the small batteries that are typically used in motorcycles.  Many of these chargers can be left connected and will keep a battery charged for months at a time.  Some models will even perform battery testing during the charging process.  Here are a few recommended battery chargers from Yuasa and TecMate:

Most of these chargers will require at least 8 hours to fully charge a dead battery.  After the charger is disconnected, repeat the open circuit voltage test.  If the battery tests less than 75% it is probably bad and no amount of charging will bring it back to life.  It may even start your motorcycle, but not with any reliability, or for very long.

If your battery’s open circuit voltage indicates a full charge, the battery can now be load tested.  Learn how to load test with a digital multimeter in our article: Motorcycle Battery Testing.

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