How To Test A Motorcycle Battery

If your bike didn't start up this morning, or if you are simply wondering how to check the condition of your old battery before it gives out on you, the answer lies ahead. There are many ways to test your bike's battery, and they don't involve going to the auto repair shop around the corner. Instead, with the right set of tools, you can run a comprehensive test on your motorcycle right at home.

Testing A Motorcycle Battery: Before You Begin

Before you start pulling out wires or calling for a battery replacement, make sure you actually have a mechanical issue. Most modern bikes are equipped with safety switches that do not produce power to the bike unless the side stand is kicked up or the clutch lever is engaged. If you tick these two off the list and still have the same result, you can follow these step to assess your battery:

  • Ensure That It’s Indeed a Battery Issue
  • Inspect the Battery
  • Use a Hydrometer or Voltmeter
  • Perform a Cranking Voltage Test
  • Repair the Battery and Find the Root Cause
  • Battery Maintenance and Storage

Remember to take every possible safety precaution, and be aware of the surroundings in your work area for items that might be flammable. If you are not familiar with the tools, then request professional assistance.

Make Sure It’s A Battery Issue

A starting issue doesn't always mean there is a battery issue. For example, if your bike's starter sounds like it might be coughing out a lung, then there might simply be a problem with the starter and not the battery itself. The quickest and easiest way you can find out if you have a faulty or dying battery is to switch on the headlights and check the strength of the light. A damaged or dying battery will often result in weaker light beams from your headlamps, which is usually a good indication that your battery may need replacing. Although this can be a good measure, it is better to move on to the next step for further diagnosis regardless of the outcome.

Inspect The Battery

Before you begin testing, it is a good practice to inspect your motorcycle’s battery thoroughly. Follow the steps mentioned below to make sure the battery is in acceptable condition:

  • Make sure your battery is dry and free of debris. Dirt sitting on top of the battery terminals could act as a restriction for current flow, causing excessive electrical discharge from your battery. You can use a soft brush to rid the battery terminals of any grime.
  • Inspect the components of your battery, such as screws, clamps, and cables for any sign of wear or corrosion. Any breakage or corrosion can interrupt the flow of electricity. Then, clean the components with a wire brush and make sure they are secured.
  • Inspect the case of the battery for any apparent damages like cracks that could leak and cause issues with the internal chemistry. For example, a raised or bloated battery case top could be a sign of overcharging or overheating.

Use A Hydrometer Or Voltmeter

You can check the state of charge on most conventional batteries by using a hydrometer to measure the specific gravity of the battery's electrolyte. After charging the battery, carefully insert the battery hydrometer into a cell. Next, press on the bulb to draw water into the hydrometer. Once filled, you can test each cell by measuring the specific gravity of the fluid. This value tells you if the cell is properly working or needs a replacement. If the hydrometer does not read the correct specific gravity level for any cell, then it is likely that your battery will need a replacement. 

In general, SG readings between 1.255 and 1.275 indicate that your battery is adequately charged, whereas a reading between 1.215 and 1.235 means you need to charge the battery. Again, make sure these readings are performed in an environment around 75 degrees.

Suppose your motorcycle has an AGM-type battery. In that case, you can use a voltmeter, an open circuit voltage test that will help you determine the level of charge in the battery and its holding capacity, along with the shorted or open battery cells. Fully charged AGM batteries will generally read at around 12.8 to 13.0 volts. A charge of between 75% and 100% will read around 12.5 to 12.8 volts. If the volt reading drops below 75% charge, then it's probably time to invest in a new battery.

Perform A Crank Voltage Test

A crank voltage test involves checking the current flow from your battery while it is working. For example, you can hook up a digital voltmeter and push on the start button. The voltmeter will give a reading of the voltage while the starter is at work. Keep in mind that a properly functioning battery should stay over 9.6 volts over around 10 seconds.

Test Recharge The Battery And Find The Root Cause

If your battery has failed one or more of these tests, then you might have to replace it. However, before you give up, it is recommended to try charging and checking the battery one more time. The most important thing to find out is the root cause of a drained battery. Things like faulty cable wires and a parasitic draw could cause the same problem to a brand-new battery. Nonetheless, simply replacing the battery and not finding the root cause more often than not ends badly.

Battery Maintenance And Storage

If your motorcycle is in storage for the winter or not used frequently, make sure to disconnect the battery cable to prevent electricity from being fed to its electrical components. Also, make sure to perform regular checks on the battery to ensure it is maintaining its charge. Keep in mind that batteries stored in temperatures below 15 degrees and over 25 degrees need to be checked and recharged more frequently.

Summary

A failing battery is a fact of life in motorcycle ownership. These are components with a limited lifetime, and they will require replacement. The test procedures listed above will go a long way in determining if the battery is good or not. However, it’s strongly recommended that you check for the root cause behind any battery discharge to avoid any potential impact on a new battery.