6 Symptoms of Bad Battery On a Motorcycle (Mechanic Thoughts)

Motorcycles have a stator that generates electricity to power the ignition system and other electrical accessories when the engine runs.

Still, a battery is necessary to run the starter for initial cranking and power the ECU (on fuel-injected bikes).

In short, modern motorcycles can’t run without a battery. A dead battery will not start the motorcycle engine. But how do you tell if your motorcycle battery has gone bad or just discharged?

This guide explains some common symptoms of a bad motorcycle battery. If you’re a motorcycle enthusiast, don’t skip this article.

So, what are the symptoms of bad battery on a motorcycle? If the battery has gone bad, your motorcycle will not start, the starter will take longer to crank the engine, the headlight and horn will not work at full potential, the battery will not hold a charge, the battery will deform its shape, and give irregular multimeter readings.

You’ll also notice corrosion on terminals, cracks or bulges in the plastic casing, and any leaking fluid or discoloration.

6 Signs of a Bad Motorcycle Battery

I believe in “prevention is better than cure.” So, instead of struggling on a ride, I’d prefer to identify the bad battery symptoms and fix them before going on a ride.

We will explore six common symptoms that indicate a bad battery on a motorcycle. These symptoms will help you identify and address battery-related issues.

1. Motorcycle Will Not Start

As I told you earlier, modern motorcycles have fuel injectors and ECUs that require electricity. It takes power from a battery installed underneath your motorcycle seat. It also powers the starter motor for initial engine cranking.

Your motorcycle will not start without a battery or if it’s faulty. So, the first symptom of a bad motorcycle battery is that your engine will not start when you press the start button.

2. Cranking Takes Longer

If you notice that the engine cranks slowly, takes multiple attempts to start, or doesn’t start at all, it could indicate a faulty battery.

It happens because the battery doesn’t supply constant power to the starter. However, if your motorcycle sits too long, it could be another reason for slow cranking or starting problems.

To ensure this, jumpstart your motorcycle and idle it for 15 to 30 minutes to recharge your battery.

If cranking is still taking longer, it’s a strong sign of a bad motorcycle battery, and you should replace it for a hassle-free riding experience.

3. Dim or Flickering Headlight

Another method to identify a bad motorcycle battery is to turn on the ignition key and look at its headlight.

If the headlight beam is dim or flickering, it’s a sign that your motorcycle battery fails to supply sufficient power.

Sometimes, the headlight flickers or doesn’t work if the battery terminals are corroded. So, inspect the battery terminals and clean the corrosion build-up with a piece of sandpaper.

4. Decreased Horn Volume

Another easy method to identify a bad motorcycle is pressing the horn switch. If the horn volume is lower than it used to or generates distorted sound, it’s a sign of a failing battery, and you should immediately replace it.

5. Battery Draining Overnight

A faulty battery will not hold a charge for too long. So, if your motorcycle battery drains overnight, it’s a sign of a battery-related issue. You should read the voltage with a multimeter, which should be above 12V.

If the multimeter reading is below 12V, you must replace the battery for hassle-free rides.

6. Battery Charging Problem

A faulty battery creates problems in charging (there are several more reasons also). A motorcycle battery refuses to charge because of sulfation or aging.

Do you remember when you replaced the battery last time? If you can’t recall, it’s an obvious indication that you need a new battery.

The average life of an AGM battery is three to four years. An older battery will create many problems. So, better you should install a new battery for hassle-free rides.

So, these are some common signs of a faulty motorcycle battery. If you notice any of the above symptoms, test your battery and replace it immediately.

How To Identify A Faulty Motorcycle Battery?

I hope you understood a lot about the symptoms of a bad battery. Now, let’s understand how to test and identify a faulty motorcycle battery…

1. Inaccurate Multimeter Reading

If you have a multimeter, please set the knob to 20V DC and connect the red wire to the positive and the black wire to the battery’s negative terminal. A good battery will give you more than 12.5V readings.

If your multimeter reading is less than 12V or fluctuates with every test, it indicates a faulty battery, and you must replace it.

2. Extreme Voltage Drop While Cranking

As I told you in the first paragraph, the starter motor takes electricity from the battery for initial cranking. So, when you press the starter switch, the battery shouldn’t drop its voltage below 10V.

If the voltage drops below the recommended value, it indicates bad battery health, and your starter motorcycle will crank the engine slowly or may fail.

3. Corrosion Or Broken Terminals

A battery provides electricity from a chemical reaction, and hydrogen gas is formed during the reaction. This hydrogen gas tried to escape from the battery casing and corrode the terminals.

If your motorcycle battery terminals are broken or have too much corrosion, it’s a sign that you must replace the battery.

4. Swollen or Bulging Battery Case

A visibly swollen or bulging battery case indicates a damaged or defective one. Over time, excessive heat or overcharging can cause the battery’s internal components to expand, leading to bulging or warping of the battery case.

5. Old Age

Generally, an AGM battery lasts between three to four years. But battery sulfation occurs when you store your motorcycle for too long, and the battery will die faster in case of deep discharge.

So, you must regularly charge the battery for longer life. I would advise you to replace your motorcycle battery every two years.

How Does a Bad Battery Affect a Motorcycle?

A bad battery will cause difficulty in cranking and starting the motorcycle engine. It also leads to poor ignition, which results in incomplete combustion of the air-fuel mixture. Hence, you get lesser MPG due to the bad battery.

Will a Weak Battery Keep a Motorcycle from Starting?

If the battery is weak or dead, it will fail to start the starter motor, which cranks the engine. If the problem is with the battery, the only viable solution to this problem is replacing the battery.

Can a Motorcycle Battery Show Full Charge and Still Be Bad?

Your battery may show full charge but fail to start the engine. A bad battery will drop the voltage or may discharge while riding. So, it’s better to replace it with hassle-free rides.

Conclusion

I’m pretty sure now you can identify a bad motorcycle battery. I have explained six common symptoms of a bad motorcycle battery. If you notice any of the above symptoms, you must inspect and replace the battery.