If your motorbike’s battery seems to be in trouble, the issue could lie in a few different areas. It might be that your battery requires charging, it could be nearing the end of its lifespan and need replacement, or the problem might not be with the battery at all but rather with the bike’s charging system.
In any event, the following guide will assist you in identifying the root cause of the problem, ensuring that you don’t get left in the lurch unexpectedly. Welcome to our bike repair guide!
Diagnosing Your Bike’s Battery and Charging System Health
The Tools Required
To gather valuable information about your bike’s battery and charging system health, there are three simple tests you can carry out.
All you need is a multimeter, which you can find online or at any hardware or auto parts store for around $30-$40. A multimeter is a highly versatile diagnostic tool, so it’s definitely worth investing in.
You’ll also need a battery charger and the relevant tools to access your bike’s battery, which typically involves just using the key.
The Initial Charging
Before we start with testing, remember that analyzing a depleted or dying battery will validate its poor state.
Thus, the first thing you ought to do is give the battery a full charge. If the battery is so drained that the charger displays an error message or never reaches a full charge, you’re probably dealing with a battery ready for the recycle bin.
However, if the charger indicates a 100% charge, take the battery off the charger and let it rest for several hours – ideally overnight.
This is because our first test with the multimeter is to verify the battery’s at-rest or static voltage. For accurate results, it’s crucial that the battery hasn’t been used recently.
Checking Static Voltage
Motorcycles and cars typically use 12-volt batteries. However, a fully charged 12-volt battery should actually display 12.6 volts, not 12.0 volts.
This is due to the battery being made up of six 2.1-volt cells. In the case of lithium-ion batteries, they should show around 13.6 volts when fully charged.
The vital point here is that the label on the battery doesn’t necessarily indicate the voltage you should be seeing – always reference a state of charge chart when dealing with your battery.
The Testing Process
To commence the testing process, set your multimeter to volts DC, denoted by a straight line symbol accompanied by dots.
Then, connect the red (positive) lead to the positive terminal and the black (negative) to the negative terminal, and record your voltage.
Note: Working around electricity might be intimidating, but there’s no cause for concern unless you accidentally bridge the battery terminals with a metal object or bridge the positive terminal to the frame, which is also connected to the negative terminal. Avoid doing these, and you’ll be fine.
If your battery registers a voltage of 12.33 volts, as per the state of charge chart for an AGM battery, it indicates that it’s only about 70% charged. If the battery has just come off the charger, this suggests that the battery is aging and losing strength.
A battery registering 12.3 volts is still functional – it can start the bike – but it’s not going to improve. The question then becomes, how long will it continue to start the bike?
Operating a motorbike with a weak battery places more strain on the charging system. Replacing those components is significantly more difficult and costly than replacing the battery.
So, while the battery might be suspect, it is still robust enough for our next procedure – the cranking volts test.
Cranking Volts Test
The cranking volts test is designed to put the battery under load with the starter motor. Therefore, we will press the starter button, but we don’t want the engine to start.
You can either engage the kill switch (if your bike still cranks when it’s off) or do what I’m doing: removing the fuel pump fuse so the bike won’t start.
Attach your multimeter leads to the battery and press the starter button for several seconds. The resulting voltage should ideally not drop below 9.6 volts. If it does, it’s a strong sign that the battery is losing capacity – it’s losing its ability to turn the starter.
Bear in mind, and all batteries have an expected lifespan of approximately four to five years. The internal chemistry begins to degrade over time.
So, if your battery is between four to seven years old and testing reveals less-than-ideal results, it’s a strong hint that it’s time to replace your battery before it fails you.
At this point, you should have a good sense of whether your battery is healthy or deteriorating. Regardless of the outcome of the initial two tests, there is a final procedure you should perform to assess the functionality of your bike’s stator and regulator rectifier.
Sometimes, a battery might be weak not because of its own fault but because the bike’s charging system isn’t functioning correctly.
Charging System Output Test
The third and final test involves starting your motorcycle to check the charging system’s output. With your leads still connected to the battery, switch on the kill switch or replace the fuse, start the bike, raise the engine speed to around 2000 RPM, and note the voltage on your multimeter.
The expected output is approximately 14.4 volts. Depending on your motorcycle, you don’t want to see anything lower than 13.5 volts and nothing higher than 15 volts. This is the voltage the bike should output to keep the battery charged while the engine is running.
If you observe a value less than 13.5 or more than 15, it suggests an issue with your stator (which generates AC when the bike is running) or your regulator rectifier (which converts the AC to DC to charge the battery and limits it to a safe 14.5 volts).
Testing the stator and the regulator rectifier is beyond this guide’s scope, but the only tool you need is the multimeter. Of course, you’ll also need the specs for your specific bike model, which you can easily find in your bike’s shop manual.
To Summarize
In brief, if you want to assess your bike’s battery and charging system health, follow these steps:
- Measure the resting voltage: You’re looking for 12.6 volts for a lead-acid battery and 13.6 volts for a lithium-ion battery.
- Stress test the battery with the starter: Ensure the voltage doesn’t drop below 9.6 volts.
- Monitor the voltage at the battery while the motorcycle is running: This gives a good indication of how effectively your bike’s charging system is operating.