Motorcycle Battery Won’t Fully Charge | Here’s Why (SOLVED)

A bike is only as good as its battery.

No matter how fresh your tires are, how fly your paint job looks, how much extra bread you spent on the stage 1 air cleaner or those stage 2 cam upgrades, none of it matters if your battery is shot.

Still, a battery can be tricky to diagnose when scratching your head and asking yourself why your motorcycle battery won’t fully charge?

Here’s why your motorcycle battery won’t fully charge:

The most common reason a motorcycle battery stops holding a charge is that the battery has expired, failed, or died. Battery materials wear in time, losing their ability to control their charge. Poor fuses or sharing system components are the next likely cause if the battery isn’t bad.

1. Your Motorcycle Battery Has Expired

The first thing to examine on a bike that won’t charge is its battery itself.

Different motorcycle batteries are constructed from diverse materials, all of which have a shelf life.

Eventually, all batteries expire; when they do, they will no longer be able to hold a charge.

There’s only one solution to a bad battery, replace it. That said, there are other reasons your battery won’t hold a charge. The battery itself might not be dead yet, only drained.

To be sure your battery is dead and not just temporality drained, let’s go over 4 Reasons Why a Motorcycle Battery Dies:

  1. Corrosion on Your Battery Terminals: If corrosion or rust forms on your battery terminals, the decay will hinder the flow of the electrical current. While, in some cases, the corrosion’s disruption is the cause that kills your bike battery, in others, the battery is already leaking and failing; the leak is the cause of the corrosion.
  2. Battery Sulfation: Battery sulfation is a particular type of corrosion that occurs if a battery is left empty for an extended period. The plates are exposed to the air if their levels are low. Air contact crystallizes the battery materials, destroying the battery.
  3. Vibration and Exposure to Heat: One of the battery-killers bikers have to live with is the fact that a motorcycle battery is more exposed than that of a car. The nature of the v-twin motorcycle motors, for example, rattles and rocks the battery around. Moto-motors run hot; the battery is often in proximity to the engine, exposing it to heat and vibration and shortening its life.
  4. Poorly Grounded Wiring: There should be a strong ground connection between your motorcycle’s battery and frame. An insufficient grounding means the battery has nowhere to dump any extra charge it’s receiving, resulting in an overcharged battery that will eventually die.

There’s not a whole lot you can do about a bad motorcycle battery—as we said up front, you’ll have to replace it.

That said, diagnosing the cause of the dead battery is essential. If a poor grounding or corroded battery terminal was the cause, you need to fix the problem, or you’ll kill the new battery in no time.
On the other hand, if the battery was just old and expired, installing the new battery might be a simple matter of plug and play… for now.

The best offense against a bad battery that won’t hold a charge is a good defense—maintaining your battery’s condition with preventive care prolongs your battery’s life and improves your motorcycle’s performance.

Here are some quick tips for prolonging the life of your battery, so it holds a charge:

  • Give your batteries’ outer layer and terminals a regular scrub to keep them all clean from engine grime and road dirt. This should be part of your standard servicing, like an oil change, at the OEM-recommended intervals.
  • While maintenance-free batteries are becoming the standard on the modern moto-market, the electrolyte levels on older batteries need to be inspected and refreshed regularly.
  • Keep your battery caps and terminals tight. Preventing fluid leakage will extend the battery’s life, and tightening the terminals ensures the connection is less affected by the motor’s vibration. Keep your battery fastened in place via your moto-manufacturer’s spec suggestions.

Cleaning your motorcycle battery’s corrosion with a wire brush or abrasive paper during your routine service intervals goes a long way in extending the life of your battery.

The owner’s manual for most motorcycles includes a battery inspection in the maintenance chart, generally at least as often as you change your oil.

If, for some reason, your bike’s service schedule doesn’t include a battery inspection and cleaning session, we suggest you take a peek at it every 3,000 miles.

If you take your bike to the shop for your standard services, go ahead and ask the mechanic to inspect your battery every time they change the oil.

To review:

  • The number one reason a battery won’t hold a charge is that it needs to be replaced.
  • It’s normal for a motorcycle battery to fail between 2 and 6 years after installation.
  • If the battery were killed by an external issue elsewhere on the bike, you’d have to isolate and fix it, or the new battery will fail.
  • Extend your new battery life by performing routine maintenance, including
    • inspecting and tightening the battery’s connectors, fasteners, and caps.
    • Inspecting and cleaning your battery and terminals every 3,000 miles with wire brush or sandpaper.
    • Examine the electrolyte levels of older batteries that aren’t “maintenance free.”

When I’m experiencing power issues on a motorcycle, the first thing I test is the battery, either with a multimeter or a voltmeter, to confirm if the battery’s drained but capable of holding a charge or if it’s truly dead. If it’s dead, I move on to troubleshooting the stator.

Related: 9 Reasons Motorcycles May Keep Stalling (Solved)

2. Your Charging System Has a Faulty Stator

Your motorcycle’s stator is the component that converts the mechanical energy generated by your motor into an Alternating Current of electrical power.

The stator generates the electrical energy that eventually makes its way to the battery to replenish its charge while you’re riding. Without the stator, the mechanical energy is wasted, and there’s no electrical current for the battery to store in the first place. 

If your stator is failing, your battery won’t hold a charge since the stator doesn’t generate a charge for the battery to hold in the first place.

Once you’ve established that your battery isn’t expired or damaged and is fully capable of holding a charge from a tender or trickle charger, the next thing to check would be the stator.

If a dead battery jump-starts, for example, the battery is OK, as an actual bad battery won’t hold a charge long enough to start the bike with a jump.

Suppose your stator is the problem and you replace the battery. In that case, as soon as the battery loses the charge it left the store with, it’ll be just as dead as the one you replaced, again, because it’s not its ability to hold a charge that’s the issue here; it’s the fact that there’s no charge being generated by the stator.

  • When I’m experiencing power issues on a motorcycle, the first thing I test is the battery, either with a multimeter or a voltmeter.
  • I test the stator next if I’m sure the battery isn’t the problem.
  • If the stator is converting the mechanical energy into an electrical Alternating Current electrical charge the way it’s intended, it’s time to move on to testing the stator.

Related: Motorcycle Clicks Instead Of Starting: 3 Reasons (Solved)

3. Your Regulator/Rectifier Is Failing

Another reason your motorcycle battery could be failing to hold a charge is a faulty regulator/rectifier.

  • The Regulator/Rectifier, or R/R, is the part of your charging system that converts the stator-generated Alternating Current (AC) into the Direct Current (DC) the battery needs to recharge. 
  • The R/R is also responsible for regulating the voltage of the DC that passes through the battery.
  • If your Regulator/Rectifier stops regulating that current, your battery can overcharge and even explode, which will no longer hold a charge.

If you replace a battery on a motorcycle with a failing Regulator/Rectifier, the new battery will incur damage in a short amount of time.

Another possible issue you might have is an R/R that fails to rectify the charge or convert the stator’s charge from AC into DC; your battery can’t use the AC.

It’s common for the cause of a motorcycle battery that won’t charge to be R/R failure impeding on its healthy functioning.

4. Your Bike Has a Blown Fuse

The fuse’s sole function is to protect the circuitry of your motorcycle. In cases where an electrical amperage surges through your bike’s wiring, the fuse absorbs the excess energy and blows to get rid of it. In blowing, the fuse sheds the extra amps before the electrical system it’s wired into incurs any damage.

Once the fuse blows, the circuit it was wired into won’t function until the fuse is replaced. A blown fuse could be why your charging system can’t charge your battery. 

Here’s how to inspect and replace a blown fuse on your motorcycle to get your battery charging again:

  1. Flip the ignition switch into the OFF position.
  2. Remove your fuse box cover.
  3. Inspect your fuses; the metal strip inside a blown fuse will be split in half, while the ribbon on a healthy fuse will be one solid piece, still intact.
  4. If you find a blown fuse, replacing it with a freshie is the only fix. Be sure you replace the blown fuse with the same rating, consulting the OEM spec in your owner’s manual to be sure. Note: Using a fuse with a higher rating can damage your bike’s electronics system, while a lower rated fuse will blow prematurely.
  5. Tampering with your bike’s electronics can cause permanent damage. If you find yourself replacing the same fuse repeatedly, the circuit probably has a bad ground, or a shorted wire. Please take it to a pro for an inspection, as electrical failures are difficult to diagnose.

Related: How To Tell If A Motorcycle Fuse Is Blown (Explained)

5. Wires in Your Charging System Are Frayed, Lose, or Shorting Out

A bad wire connection in your charging system will undoubtedly make it seem like your motorcycle battery won’t hold a charge.

These days, your standard motorcycle uses multiple breakers to protect your bike’s electronic circuitry, including:

  • Main
  • Lighting
  • Ignition
  • Gauge Cluster
  • Electronic Accessories

These breakers can reset themselves to prevent damage, sending stable power back to the circuit once the electrical failure is rectified.

If the failure remains in effect, the breaker’s cycling is sporadic, causing the bike’s operations to be intermittent until eventually, it kills the battery.

Again, we suggest taking a bike with electrical failure to a pro, as electrical systems are a unique science.

Frayed wires can cause severe damage, not just to your charging system but also to your ignition circuitry, which affects motor functions.

Suppose you suspect that a broken wire is the reason your motorcycle’s battery won’t hold a charge. In that case, there’s no shame in taking it to a mechanic who’s literate in your make and model motorcycle electrical systems.

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