Motorcycle Battery & Charging System

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Understanding your motorcycle’s battery and charging system is the core to understanding your bike’s electrical system.

This page will cover all the basics to get you started.

But first – as with any electrical task on your bike, it’s good to have a multimeter handy.

A multimeter will allow you to measure voltage and continuity between wires on your bike.

Motorcycle Charging System

Motorcycle charging systems typically consist of 3 main compnents:

  • Battery.
  • Alternator/stator.
  • Regulator/rectifier (either combined or separate components)

The battery is the voltage center of the bike and stores the DC current.

The alternator or stator is connected to the crankshaft and spins as the engine’s crankshaft spins. The rotation generates alternating current (AC) as it moves.

The regulator ensures that voltage stays in the necessary range.

The rectifier converts AC to DC.

How to Check Your Motorcycle’s Charging System

Checking that your motorcycle charging system is working is fairly simple.

You’ll need a multi-meter set to measure DC voltage.

To check your charging system:

  1. Place the black wire from your multimeter to the negative terminal on your battery.
  2. Place the red wire from your multimeter to the positive terminal on your battery.
  3. Check the voltage reading.
    • A good, charged battery should read around 12.4 DCV.
    • A battery with a lower reading may need to be charged or may be dead.
  4. If the battery is good, turn on your bike, start the engine, and let it idle.
  5. Read the voltage again. It should increase to about 13 to 13.8.
  6. Increase the RPM to about 3,000 and hold it.
  7. Read the voltage again. It should increase further (about 14-14.6 DCV).

If your stator/alternator is bad, you likely won’t see any voltage changes when the bike is on and RPMs are increased.

If your regulator is bad, you will see voltage higher than 14.8v or so. This can overcharge and damage the battery.

If your rectifier is bad, you may not see a change in voltage at the battery as the AC from the alternator won’t be converted to DC for the battery.

Motorcycle Batteries

Motorcycle batteries are the electrical center of the bike.

Most motorcycles have a 12 volt battery, while smaller bikes and scooters may have a 6 volt.

How does a motorcycle battery charge?

A motorcycle battery gets charged when the engine is running.

As the bike runs, voltage is drawn from the battery to electrical components on the bike.

As the crankshaft turns, AC voltage is created at the stator/alternator and is sent through the rectifier to turn it into DC to charge the battery.

A bike that hasn’t been running or won’t run for a while, may need its battery placed on a trickle charger to maintain the voltage.

Does a motorcycle battery charge while idling?

A proper charging system should provide some amount of charge at idle.

Ideal charge is achieved at RPMs at around 2,500 – 3,000+.

How long will a motorcycle battery last without charging?

If a motorcycle battery isn’t charged, it will lose power over time.

Most batteries will die after about 2-5 months with no charge and not being run.

Motorcycle batteries drain at a rate of about 1% of charge per day it doesn’t run.

Can you lay a motorcycle battery on its side?

Absorbed glass mat (AGM) and lithium ion motorcycle batteries can be on their side.

Traditional lead acid batteries need to be installed upright.

When should I replace my bike’s battery?

You should replace your battery if it won’t hold a charge.

Batteries naturally degrade overtime, as well.

Most batteries need to be replaced about every 4-5 years.

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