Why Would Motorcycle Battery Get Hot?

Did your motorcycle fail to start this morning and you just found out that your battery gets pretty hot? Or worse, you smelled something burning and found out it’s coming from your battery. 

That can’t be good – right? Why is your battery getting so hot? If that’s what you are experiencing, then you are definitely not alone. 

This can happen sometimes and I am just surprised how nobody is writing about this yet. So here we go. 

In short – motorcycle batteries get hot because they’re overcharged. And this usually happens because you have a faulty voltage regulator or corroded terminals. Keep this up and your battery will likely be roasted or even blow up. 

Let’s talk more about batteries and overheating. Beginning with voltage regulators – what even is that?

Voltage regulator is a device that regulates the amount of voltage coming into your battery. This is done because the voltage generated by the alternator is not the same as the electrical components in the motorcycle.

Did you get that? Probably not. Let me try again.

A battery exists in your motorcycle to power electrical components like headlights, blinkers and other things. These electrical components operate at a constant voltage (usually 12 V). 

When your motorcycle is running, it constantly charges the battery using an alternator. Alternators may produce electricity at different voltages – the higher the RPM, the higher voltage is generated (can even go up to 15-20V).

This voltage clearly won’t work well with the electrical component in your motorcycle. They operate at 12V but the alternator is supplying electricity at a higher voltage than that. 

This is where a voltage regulator comes in – it’s responsible for ‘regulating’ the electricity input into the battery to an expected operating voltage. 

This way, regardless of how much voltage the alternator is providing, the voltage that’s supplied by the battery to other electrical components is always correct and expected.

Image of voltage regulator

Now that you know what voltage regulator is, let’s talk about what happens when it fails. Faulty regulators are the most common cause of overheating batteries but they are not always the case.

1. Faulty Voltage Regulator

A faulty voltage regulator is the most common reason for battery overheating. When the voltage regulator is not working, electricity coming into your battery from the charger may have a higher voltage than expected. 

This means your battery is taking in more voltage than it should – causing it to overcharge and overheat. 

There’s also a chance for other electrical components to break. Similar to the battery, every other electrical component in your bike expects a lower voltage.

If your battery is receiving electricity at a higher voltage, the battery will also supply electricity at that higher voltage. Electrical components in your motorcycle will not expect this higher voltage and could break. 

Voltage regulators are pretty cheap. The only fix to this problem is to replace it with a new one. If you don’t understand what I am talking about, read the function of voltage regulator above. 

2. Corroded Battery Terminal

Corrosion in battery terminals acts as a resistance for electricity to pass through. Electricity that is blocked by the corrosion turns to heat – causing your battery to overheat (especially during start up). 

Corrosion in battery terminals is a normal occurrence – just make sure you regularly take the terminals off and clean them. Then you will be safe from these problems.

Corroded battery terminals

3. Faulty Battery Cell

A faulty battery cell in a motorcycle battery will cause the other battery cells to take on more charge – causing them to overcharge and overheat.

Batteries are always made up of multiple battery cells – each of them capable of taking some charge that totals to 100%.

Should any of these battery cells malfunction, they wouldn’t be able to take any charge. The battery charges will assume that the battery is not fully charged yet and keep supplying electricity – causing the rest of the cells to overcharge and overheat. 

4. Incorrect Battery Size

Using a battery that’s smaller than intended for your motorcycles can cause it to overcharge and overheat. 

Did you happen to just replace your battery and notice your battery overheating? If yes, then I recommend you checking the size of that battery. Could be smaller than intended – thus overcharging. 

5. Faulty External Charger

Using an external charger that’s faulty could cause your battery to overcharge and overheat. The external charger could have an irregular electrical flow and overcharges your battery. 

When you have battery problems, it’s best to get it checked out by a shop. Using old external chargers that could be faulty is not wise. 

Now that you know what may cause battery overcharging and overheating, let’s talk about what happens if your battery is left to overheat over time. 

This should motivate you to get that battery issue fixed (or at least checked out by a shop). 

1. Risk of blowing up. This is the worst case scenario. The battery overcharges and overheats too much to the point it explodes. Keep in mind that the battery in your motorcycle is just underneath your seat (dangerous waters). 
2. Dead battery.  This is quite common. Your battery has been overheating for sometime without you knowing. It could just die and not start up your bike anymore. 
3. Shorten batten lifespan. This is a given. Overcharging and overheating your battery is not healthy at all. In the best case, you will just damage some cells. Your battery will no longer be as powerful but it will still work (for some time).
4. Speeds up battery corrosion. Hot battery helps in building up corrosion. And you already know what happens when battery terminals are corroded – the battery gets even hotter because electricity can’t flow. It’s like a closed loop of heat generation.
5. Battery boilover. Battery boilover is when your battery gets too hot and it starts boiling the water and acid inside the battery. Without enough battery and acid, your battery will no longer work.