A motorcycle battery is small and easy to overcharge. A car charger can cook it; a cheap trickle charger can boil it dry. A smart charger that senses the battery's state and tapers the current is the safer choice for a bike that sits between rides.

SystemWorkshop equipment
Typical materialsTransformer or switch-mode charger with control circuitry
What to checkOutput voltage, charge rate, chemistry compatibility and cable condition
Technical schematic of Motorcycle battery chargers
Fig. 01 — working principleIndoBikes drawing

What it is for

The charger pushes current into the battery to reverse the discharge process. A maintainer holds the battery at full charge without overcharging. Some chargers also test and recondition.

The charger must match the battery's chemistry and capacity. A lead acid battery and a lithium battery need different charge profiles. A charger that is too powerful for a small battery can overheat it.

How it works

A smart charger measures voltage and adjusts current in stages: bulk, absorption and float. It may also pulse to reduce sulphation. The charger should stop or reduce output when the battery is full.

A battery that is deeply discharged may not accept charge at first. Some chargers will not start on a very low battery. A battery that will not hold charge after a full cycle is usually worn out.

Types and variations

  • Trickle charger. A low, constant current. Simple, but can overcharge if left on.
  • Smart charger. Senses the battery and tapers the charge. The usual choice.
  • Maintainer. Keeps a charged battery at float voltage. Good for stored bikes.
  • Jump starter. A high-current pack for starting. Not a charger.
  • Lithium-specific charger. Uses the correct profile for lithium iron phosphate batteries.

When it stops being reliable

  • A charger that does not reach the expected voltage.
  • Crocodile clips that are loose or corroded.
  • A cable that is cracked or has exposed wire.
  • A charger that overheats or smells hot.
  • A maintainer that never switches to float.
  • A battery that will not hold charge after a full cycle.

Choosing one

  • Choose a charger rated for motorcycle battery capacity, often 1 to 4 amps.
  • Match the charger to the battery chemistry.
  • A smart maintainer is better than a constant trickle charger for a stored bike.
  • Check that the charger has reverse polarity protection.
  • For a lithium battery, use a lithium-specific charger.

Range and compatibility

  • Connect the charger to the battery before switching on.
  • Connect the positive lead first and the negative last.
  • Charge in a ventilated area, away from sparks.
  • Do not charge a frozen battery.
  • Disconnect the charger before removing the leads.

Accuracy and care

  • Keep the charger dry and the leads clean.
  • Do not leave a cheap trickle charger connected indefinitely.
  • Check the battery voltage after charging.
  • Store the charger indoors.
  • Replace damaged leads.

Safety and limits

Batteries produce hydrogen. Charge in a ventilated area and keep flames away.

A charger can cause a spark. Connect and disconnect in the right order.

Do not charge a swollen or damaged battery. Replace it.

Questions

Can I use a car battery charger on a motorcycle battery?

Only on a low setting and only if it is suitable for the chemistry. A high-rate car charger can damage a small battery.

How long does it take to charge a motorcycle battery?

It depends on the charger and the battery's state. A 1 amp charger can take many hours for a discharged battery.

Can I leave a maintainer connected all winter?

A smart maintainer is designed for that. A simple trickle charger is not.

Do lithium batteries need a special charger?

Yes. Use a charger with a lithium profile and check the battery maker's instructions.