A motorcycle battery is the first step in firing up your starter and sparking your engine.
Once your motorcycle is up and running, your charging system converts engine power into a current the battery can use to recharge, regulating the current so the battery never draws more energy than it can handle.
If your motorcycle battery is getting hot, there’s an issue with your charging system, motorcycle circuit, internal battery circuit, and engine cooling, all of which can cause severe problems risking the motorcycle’s performance and the rider’s safety.
Let’s look at the most common reasons a motorcycle battery gets hot.
1. Internal Short Circuit in Battery
The battery comprises a series of cells that integrate into the operational battery.
Each cell generates a voltage of 2.1 when the battery is charged to completion and fully functional.
- Suppose any other items on the listed damage the battery.
- In that case, the connection between the individual battery cells could be compromised, causing a shortage in the inner circuit.
Once the battery has a short circuit internally, one faulty cell can trigger a chain of surrounding cells taking more charge than they need to compensate. The battery will continue to get hot well after it’s fully charged, even after you’ve repaired the issues that caused the cell damage in the first place.
A motorcycle battery that overheats due to compromised inner circuitry needs to be replaced, or the poor connection can cause electrical damage elsewhere, and your engine performance will suffer.
2. Excessive Motorcycle Vibrations
Some motorcycle engines—air-cooled v-twins, for example—are already prone to causing solid vibrations due to the nature of their combustion-powered pistons.
Suppose the motorcycle is ridden on rough roads. In that case, the suspension, fork, or wheelset are unaligned, or if there’s an engine failure causing more vibration than usual, the battery cells are jostled around enough to heat your motorcycle battery.
If the shaking is strong enough to disconnect the battery cells from the battery plates, the unhinged plates can make contact and short out until your bike battery overheats while riding.
3. Extreme Cold Froze Battery’s Electrolyte
There are different motorcycle batteries, some of which use battery fluid called electrolyte.
If the motorcycle is stored at extremely low temperatures with a battery that isn’t fully charged, the juice inside the battery can freeze.
Once the battery’s electrolyte fluid freezes, the frozen juice expands, warping the battery plates.
If the bent battery plates touch each other and remain in contact until the bike is taken out of storage, they will short out as soon as you attempt to charge it, overheating the motorcycle battery.
4. Extreme Heat Evaporates Battery Fluid
You may have wondered why your motorcycle is often easier to start in the summer than in the winter—one of the reasons is that heat increases the electrolyte’s reaction inside your battery.
That said, if your motorcycle is stored or ridden in scorching climates for a prolonged period, especially if it’s ridden hard, the water content in the battery fluid can boil out and evaporate.
If extreme heat evaporates your electrolyte’s moisture, dropping your motorcycle’s battery fluid levels, your battery’s energy output will drop, causing it to get hot.
The hotter the battery gets, the more its fluid evaporates and lowers its electrolyte levels. This becomes a perpetual cycle of overheating that can melt your battery parts and even fry or blow up your motorcycle’s battery.
Note: A heat-damaged battery must be replaced before riding your motorcycle, or you’re risking severe damage to both the bike and the rider.
5. Motorcycle Battery Damaged During Manufacturing or Transportation
While motorcycle battery manufacturers test their batteries for weaknesses, not every battery is tested.
Furthermore, some defects don’t manifest until the battery has been discharged and replenished for a few cycles and the battery gets hot.
In other cases, the motorcycle battery is shaken violently during the transportation process, whether in the motorcycle or shipped in a jostling box full of batteries.
And finally, if your motorcycle battery was stored in a hot or cold warehouse before it made its way into your motorcycle, it may have developed an internal short circuit and overheated.
6. Failing Regulator/Rectifier
Your motorcycle’s charging system is a simplified version of a car’s alternator.
It includes a stator that converts engine power into voltage current to recharge the battery while you ride.
It also incorporates a part called the Regulator/Rectifier. As its name implies, the regulator/rectifier rectifies the stator’s current to assimilate with the battery’s.
The R/R also regulates voltage flow, so the battery doesn’t overcharge once full, even though the stator steadily converts usable voltage from the engine.
If your regulator/rectifier wears out, overheats, or fails to convert and govern the current flow from the stator to the battery, your motorcycle battery can overcharge and get hot.
- The Regulator/Rectifier is part of your motorcycle’s electrical network; if it fails, you may notice more electronic accessories, such as lights, ignition, and starter systems, malfunctioning.
- If the battery is overcharged, the current it provides to the rest of your electrical system can become erratic, which may cause wires to short out and melt and fuses to blow.
- Therefore, a faulty Regulator/Rectifier should be repaired before riding, especially if you’ve noticed your battery is hot.
You might also be interested in our article about reasons a motorcycle isn’t running smoothly.
7. Battery Terminals Are Compromised
If your motorcycle’s battery terminals are corroded or poorly connected, or if the connection is interfered with by dirt, grime, or moisture, the interference causes resistance to the electrical current. The trapped current generates heat that causes your motorcycle battery to get hot at startup.
- It may be as simple as tightening the battery terminals, but we suggest you start the troubleshooting process with a detailed inspection of your battery terminals and wires.
- Unhook the positive side first, then the negative.
- Inspect all the connections for corrosion, dirt, moisture, or frayed or melting wires.
- Clean, repair, and replace the faulty components accordingly.
- Re-tighten your terminals to spec.
- Check your battery terminal connections during routine maintenance, often after you’ve ridden on rough roads, in harsh conditions, or experienced intense vibrations for any reason.
Please also read our article about reasons motorcycle battery won’t charge while riding.
8. Using the Wrong Battery for the Bike
Motorcycle batteries are not interchangeable, and using the wrong size, capacity, or chemistry type can cause the battery to overcharge and get hot, both at start-up and while riding.
Not all motorcycle batteries are created equally; lithium and electrolyte batteries, for example, all charge differently.
While most motorcycles require a 12-volt battery to start and run correctly, dirt bikes, ATVs, and other bikes may use a 6-volt battery that looks similar in size to your motorcycle battery but charges at a different voltage.
- Motorcycle batteries have varying quality and grade, and using a lower rate than your moto manufacturer suggests can cause improper charging, power loss, and overheating.
- Motorcycle batteries also vary in their capacity—two 12-volt batteries may have entirely different AMP or Hour ratings, despite the same voltage rating.
- You are using a battery with fewer AMPs than your bike calls for, causing the battery to get hot and fail.
- Finally, batteries are made from different chemical materials; lead plates and acid, lithium, and electrolyte gel batteries are the most common on today’s bikes.
- These materials charge and behave differently and, therefore, aren’t always interchangeable from bike to bike.
9. Faulty Battery Tender or Trickle Charger
If your motorcycle battery gets hot when connected to an external battery tender or trickle charger, the battery tender or trickle charger might be bad.
If you don’t experience overcharging or overheating when your battery charges via your charging system while driving; the external battery charger may be why your bike battery overheats.
Some tenders are of lower quality than others, wearing out after a few uses or if they’re left plugged in for too long.
- In the previous section, we talked about the various batteries motorcycles equip. Some of these batteries require specific kinds of chargers.
- It might not be that the tender is faulty, but it’s meant for other battery types.
- Using a trickle charger meant for a lead acid battery to charge a lithium-ion battery can overheat a lithium battery until it melts—I’ve seen it happen.
A short, faulty connection or electrical failure in the battery charger can cause erratic power transfer and current blockages that generate heat and cause your motorcycle battery to get hot while charging.
- First, test the battery itself to see if it’s still good.
- If the battery is still good, you likely have a faulty trickle charger or battery tender on your hands.
- That said, just because the battery tests poorly doesn’t mean the charger isn’t the reason it’s failing. Replace the bad battery, but test the new battery before you hook it up to the questionable charger.
- Once you’ve confirmed the battery is good and suited for your specific make and year model motorcycle, use it until it’s empty.
- Recharge the battery on your external charger after confirming the tender you’re using is appropriate for the specific type and capacity battery you’re attempting to charge.
- Pay close attention to whether or not the battery overheats while charging. Don’t leave the charging battery unattended if you suspect your charger is faulty.
- If the new battery gets hot and fails, the charger is likely the culprit, especially if you’ve already confirmed the battery was in working order.
Make sure to check out our article about reasons a motorcycle won’t start after a long winter.
10. Aftermarket Accessories Overloading Your Battery
As we mentioned a few times now, not all batteries are interchangeable.
The battery your motorcycle spec calls for is the particular capacity required to power and maintain the functions of your electrical accessories, such as light, GPS, stereo, locking bags, and alarms.
If you add a significant amount of aftermarket electrical accessories to your motorcycle, you increase the draw on your battery while riding and while your bike is parked.
If your motorcycle’s battery system isn’t reinforced to handle the excess draw of aftermarket accessories, your battery gets hot, overcharges, overheats, and eventually fails for good.