Charging a motorcycle battery with a car charger

In this post, we will show you how to charge a motorcycle battery with a car charger fast and easily. But there are some things to consider first.

Most motorcycles nowadays utilize the 12v electrical system the same as cars do. This means it is safe to use most 12v car chargers on a 12v motorcycle battery. Problems may arise if you try and charge these small-capacity motorcycle batteries with a high charge rate designed for big car and truck batteries.

I use a 12v smart charger from Ctek, which is a multi-step charger designed to keep your battery in tip-top condition. This is so the battery will last many years. It has a few different charge rates for small and big 12v batteries.

It is important to charge your motorcycle battery at the correct charge rate, usually under 3 Amps. Read on for more information so as to not destroy your small motorcycle battery with excess power.

How to charge a dead motorcycle battery

How to charge a dead motorcycle battery
My quick disconnect charge lead on the Yamaha MT07

There are a couple of ways to charge a dead motorcycle battery. You can fully remove the battery and charge it up with a 12v charger or you can attach a set of fly lead plugs to the battery terminals.

I prefer the fly lead method as some batteries are hidden and require the removal of side panels and plastic covers. These fly plugs can be bolted onto the battery and left on for the life of the battery.

Best motorcycle battery charge rate at 12v

ctek vs noco group shot g3500

As motorcycle batteries are much smaller than car batteries they must be charged at a slower rate. This will prevent gassing and overheating of the battery.

It is best to charge motorcycle batteries at 2 amps or less. This rate will give you the best conditions to charge your motorcycle battery.

Many 12v smart chargers will have a motorcycle or small battery setting that will restrict the current to the battery. I use a Ctek smart battery charger for my Harley Davidson motorcycle and my Yamaha MT07. But it can be used for any motorcycle or car.

As motorcycle batteries are much smaller in size and capacity it is best to charge them at a rate of 2 amps or less. I just can’t stress this enough.

How long to charge a motorcycle battery at 2 amps?

Depending on the size of the battery and how discharged the motorcycle battery is, it could take up to 10 hours to charge a motorcycle battery fully.

Let’s say for example if you have a YTX20L-BS 12V/20Ah battery. This is a 20Ah battery at 12 volts. So if your charge rate is 2 amps then 2Ax10H = 20Ah.

If your charge rate is 1 Amp then it will take 20 hours to charge a 20Ah motorcycle battery.

This is the safest way on charging a motorcycle battery with a car charger.

Charging a motorcycle battery with a car battery, is it safe?

Charging a motorcycle battery with a car battery, is it safe? Yes
Car Battery Charger Fly Lead Connected to Motorcycle Battery

It is not recommended to charge a motorcycle battery by using a car battery. This is because there is no regulation of the charge rate and you can easily pump in over 10Ah by a direct connection to a car battery.

It would be ok for a few seconds if you are jump-starting your motorcycle from a car battery but no longer. Excess gassing and overheating will be a problem for the smaller battery.

How to charge a 6-volt motorcycle battery

You cannot use a 12v battery charger to charge a 6v motorcycle battery. You will have to purchase a dedicated 6V battery charger for the task.

Some smart chargers have a setting that allows you to switch between 6v and 12v. Some old Triumphs have a 6v electrical system and people are converting them over to 12v systems with new alternators and rectifiers. So it may be easier to buy a dedicated 6v battery charger.

Charging a 6V battery is the same as a 12V battery. Just make sure to use the 6V selection switch. You will find that the charger may output around 7V to fully charge the battery. As always keep an eye on the battery for the first 10 minutes to make sure everything is fine and there is no excess gassing or heat generation.

Can you charge a motorcycle battery while still connected

Can you charge a motorcycle battery while still connected
Charging a motorcycle battery while still connected to a Yamaha MT07

Yes, you can charge a motorcycle battery while it is still connected. In fact, many smart battery chargers supply a fly lead to permanently connect to your battery.

I have a Ctek fly lead plug connected to my Yamaha MT07 which sits just under my passenger seat. This way only the seat needs to come off when the battery needs a top-up.

Charging a motorcycle battery with a car charger is safe as long as you use the small battery setting or charge at 2A or less.

This is the same as the motorcycle alternator charging the battery while it is connected. The motorcycle electrical system can handle the higher charge voltages of around 14v.

If you notice any acid leaking from your battery you will need to remove it from your motorcycle and wash down the spilled acid otherwise it will corrode metal and plastic parts.

How to revive a dead motorcycle battery

How to revive a dead motorcycle battery
Using the recondition feature on the Ctek battery charger to repair a dead battery.

The only way to revive a dead motorcycle battery is to use a car smart battery charger using the recondition feature. This setting will pulse a higher voltage into the battery usually around 16v and above for a short time.

This pulsing will shock the sulfication build-up on the lead plates that is causing a dead battery.

It is best to remove the battery from the motorcycle while you are reviving it so you can check the battery’s acid level. If you notice any deformation of the battery walls or excess heat generation stop charging and dispose of the battery safely.

Overcharging and excess gassing of lead-acid batteries can produce sulfur, and hydrogen sulfide (H2S), which is a possible by-product. This is why you should charge the battery in a well-ventilated area if it is old and you are doing a recondition.

Most motorcycle batteries will only last around 3-5 years due to vibration, heat, stop-start charging, and acid levels. Replace your battery if it is over 3 years old.

Does a jump starter charge the battery?

Yes, a jump starter will input a small amount of charge to the battery but most of the jump-starting power will go directly from the portable jump starter to the starter motor of the vehicle.

I have this wireless jump starter for all of my cars and motorcycles as it is one of the best on the market at a cheap price. Plus it charges my iPhone wirelessly.

It is handy to have a charger and a jump starter for emergencies.

Why Does a Lead Acid battery go flat over time?

A lead-acid battery will slowly discharge over time even when not connected to any electrical devices. On average a Lead Acid battery will self discharge around 40% a year in optimal conditions. I have heard of discharge rates at around 1% a day in very hot/cold conditions and poor battery water levels.

This is why a battery tender must be high on your list if you will store your motorcycle for long periods of time.

Alarm systems and computer-controlled motorcycles often have a small amount of current flowing from the battery to keep the systems awake. This will cause your battery to go flat faster.

Does a motorcycle battery charge while idling?

Yes, a motorcycle battery will charge while it is idling but at a slower rate. It is best to go for a ride for 20 minutes to quickly charge up the battery.

While the motorcycle is idling the alternator and rectifier will be outputting 12.5v to 14v but at low amperage. You will need to spin the alternator faster to pump out a higher current for the battery to charge quickly.

So take it for a long ride and vary the RPMs of the engine keeping it on the higher side. Once you get it home give it a start in a few hours to make sure it has held the charge.

Can you jump-start a car with a motorcycle battery?

Yes, you can but due to the small area inside a motorcycle, it is best to remove the motorcycle battery before jump-starting a car or another motorcycle. Due to the lower cold-cranking amps, a motorcycle battery will turn over a car starter motor slower. I would recommend leaving the motorcycle battery connected to the car battery for a few minutes before trying to start the car.


If your battery is flat see if you are able to charge the motorcycle battery with a car charger. Only use it if you can drop the charge rate to 2 amps or less.

If you are in a jam you can use a higher charge rate but only for an hour. Let the battery cool down for a few hours and then top up again for an hour.

Continue to monitor the battery acid level and the battery shape. If there is any deformation and excess gassing stop.

If your motorcycle battery is over 3 years old consider replacing it. Here is the Yamaha MT-07 battery replacement procedure if you would like to know how it is done.

Remember all information supplied here is what has worked for me. your circumstances may be different with different appliances. Always take appropriate care when working with electricity and acid. Wear the appropriate personal protective equipment.

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  1. My brother has been thinking about getting a battery charger for his motorcycle in order to be safer. He would really like to get some help from a professional in order to be more effective. I liked what you said about how idling the bike can charge the batter even if it is slower.


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