Your bike has been standing for a couple of months and now the battery is dead. I know the feeling all too well. The question now is: “Will my bike run with a dead battery? What about running without a battery altogether?”.
An older motorcycle with a magneto and a carburetor will most likely run fine without a battery. Modern motorcycles with an alternator and electronic fuel injection will most likely not run without a battery. There are, however, a lot of variables that will determine whether you bike will run without a battery, so in short: “It depends.”
Whether your motorcycle will run with a dead battery or without any battery at all depends on a lot of factors. I did some research on the matter and I will try my best to explain what I’ve learned, but in the end, your bike may be different.
I’ll address two questions in this post. Firstly, will a bike without a battery start, and Secondly, will it run.
Will a Motorcycle Run Without a Battery?
What a strange question. Don’t worry, I don’t judge. I am guessing that either your battery is dead and you wonder whether you’ll be able to ride without it… or, you are building/restoring a bike and would like to run the bike without an ugly battery.
Regardless of your reasons, this question does not have an easy ‘yes/no’ answer. Before I start explaining what I’ve learned, let’s quickly chat about the function of the battery.
Function of the battery
The main function of your motorcycle’s battery is to store electricity in order to start the bike. Most modern motorcycles have electric starters that need 12V electric current from a battery to spin the starter motor.
The electricity stored in the battery is necessary to power other electrical systems too, especially on modern motorcycles with electronic fuel injection (EFI), electric fuel pumps, various sensors and an immobilizer.
Once the engine is running, the alternator provides the current necessary to operate all the electrical components like headlights, indicators, the fuel pump, electronic injectors, the computer controlling the ABS and traction control, etc.
An alternator provides alternating current (AC), while all the systems on the bike requires direct current (DC) to operate. The AC will fry the systems if it was not converted to DC somehow. That’s what the rectifier does.
The alternator generates AC and the rectifier converts it to DC to charge the battery and power the bikes electrical systems. Any excess current that is not required by the motorcycle’s components are sent to the battery to charge it. The battery stores this electricity for starting later on, as well as reserve electricity for when the alternator cannot provide enough current.
The alternator generates power in proportion to engine speed. This means that when you are riding slowly in traffic or idling the motor, the alternator may need some help from the battery to provide enough juice to the electrical system.
When the engine rpm is high, the alternator runs all the systems and the battery absorbs the excess current. When the engine rpm is low, the battery supports the alternator by providing the shortfall.
On older bikes with carburetors and no fancy electronics, a battery is not necessary to start the bike. If the bike has a kick starter, most classics would fire up even with the battery completely removed. I ride my 2013 Yamaha AG 200 without a battery.
Whether your motorcycle will run (or start) without the battery, depends on your bike’s charging, ignition, and fuel delivery system.
Older motorcycles, especially scooters and other small 2-stroke bikes, use a magneto to generate electricity to ignite the sparkplug. Although not the primary function of the magneto, it also generates enough power to charge a battery for starting.
That’s why it is not uncommon to see older dirt bikes run without a battery at all. I’ve got a 1979 Yamaha MR 50 that has never had a battery in it since I bought it more than 10 years ago.
More modern bikes either use a stator or an alternator to generate electricity.
Stators are similar to alternators, but are contained within the engine case. A stator has a permanent magnet, which means it does not need a 12V electricity source to excite (or activate). A motorcycle with a stator is more likely to start on a flat battery by pushing it than a bike with an alternator.
On motorcycles with an electric fuel pump and a stator, you might be able to push the bike fast enough down a hill in order to get the fuel pump to prime the system.
An alternator is an externally mounted component with an electro-magnet. The alternator is usually driven by a belt (like in a car) or a gear, and generates AC current to charge the battery and power the bike’s electronics. Running an alternator without a battery could damage sensitive electronic components at high rpms.
A motorcycle with an alternator is usually not possible to push start and you’ll need a jump start from a battery pack like this if you have a flat battery.
Fuel delivery system: Carburetor vs EFI
Starting and running a motorcycle without a battery is not just about the charging system it has. The way in which the air-fuel mixture is delivered to the engine plays a big role.
On motorcycles with carburetors (most classic bikes and many dirt bikes), there is no electric fuel pump. Fuel is sucked into the intake manifold and combustion chamber by airflow or vacuum. The carburetor float bowl is then filled up through the needle and seat which is operated by a float (similar to a toilet cistern).
Gravity feeds the gas from the fuel tank to the carburetor float bowl. Bikes with carbs are generally much easier to start without a battery. As long as the charging system is able to deliver electricity to the ignition system, thereby firing the spark plugs, the carb will deliver the fuel.
On new motorcycles with electronic fuel injection (EFI), you might not get so lucky. These systems are fed by a high-pressure electric fuel pump which requires 12 volts to run. The injectors often also need electricity to discharge and there are various sensors feeding info to the ECU which has to calculate the air-fuel mixture.
On some motorcycles you might be able to push start the bike if the battery has enough juice to power the EFI system. You’ll have to press the started button as you dump the clutch though.
If you remove the battery completely, you won’t be able to start an EFI bike. Even if the bike starts, it will likely not run well without a battery as some electronics won’t run well at low voltages.
Ignition system: Points vs CDO vs TCI
We are getting technical now and I am no expert, but the type of ignition system your motorcycle has will also affect whether (or how well) it will run without a battery.
Only the really old classic motorcycles use contact breaker ignitions. Older bikes often have a capacitor that enables the bike to be kick started and run without a battery too. If you have a modern bike, you won’t be running a contract breaker ignition system.
Most motorcycles have a capacitor discharge ignition (CDI) module that manages the spark generation and timing. CDI ignition does not require a lot of power and is not dependent on duration it received power for. That means you will often be able to push start a bike with CDI ignition, provided the fuel system allows it.
Another type of ignition found on modern motorcycles is the transistor coil ignition (TCI). These systems need more power than a CDI and is also time-dependent. This means that the TCI unit needs electricity for longer than a CDI in order to fire the spark plugs properly.
A bike with EFI and TCI will be hard (if not impossible) to start without a battery.
Will a Motorcycle Start Without a Battery?
This is an all too familiar scenario. Your bike has been standing in the garage all winter and now the battery is dead. Of course, you can charge the battery and if it holds charge, no worries. Right? But what if it is permanently dead. How do you start it?
Even without a kick starter, it could be possible to push start a motorcycle without a battery. This will depend on the systems and whether they need DC voltage to operate. On old motorcycles with a magneto charging system, a few turns from the rear wheel should be enough to power up the ignition system to give a spark strong enough to fire up the engine.
Modern bikes with alternators may not be able to start by pushing it. That said, if the battery has some juice left, and you push your modern fuel injected bike down a long enough slope in order to build up enough charge in the system, you may get lucky.
To read more about starting a modern bike with a flat battery, check out this post I wrote.
How to Start a Motorcycle With a Flat Battery
Okay, so your battery is flat but not completely dead. Let’s briefly look at a few good ways to get the motor running.
Jumpstart from another bike or a car
After fully recharging or replacing the battery, the best way to start your bike is to jumpstart it from another bike or car’s battery.
Connect the positive of your bike to the positive of the donor vehicle’s battery using thick jump leads. Next, connect the negative to the donor’s negative terminal, and the other end to your battery’s negative.
Start the donor vehicle and then start your bike using the electric start button. It is a good idea to switch on your headlights before cranking your starter to prevent a sudden spike of current to damage any sensitive electronics.
Jumpstart from a booster pack
If you travel alone to deserted areas, jumping from another vehicle may not always be an option. That’s why it is a good idea to carry a booster pack like this in case of an emergency. Connect positive to positive and negative to negative, crank your starter, and off you go.
Obviously, if you have a kick starter you are in luck. That’s why I prefer motorcycles that have both electric start and kick start. The problem is, very few modern bikes come with a kick starter.
When my wife and I travelled through the length of Africa for three months from Cape Town to Cairo, we rode two 200 cc Chinese delivery bikes. One of the main advantages was that they had electric start and kick starters. That, and parts are freely available all across Africa.
As a last resort you can try to push start your bike. Make sure the ignition switch is in the ‘On’ position and the kill switch too. Push the bike in second gear with the clutch pulled in. If you don’t have a downhill, you might need a friend to help you.
Once at speed, jump on the seat (for the rear wheel to grip instead of lock up) and dump the clutch. If they bike starts up, immediately grab the clutch to prevent it stalling or riding off without you.
If your bike is fuel injected, you may have to press the starter button at the same time as dumping the clutch, but your chances of getting your EFI bike to fire up is slim. Rather phone a friend.
How to Prevent a Battery From Going Bad
Flat batteries are super annoying. The best way to prevent it is to keep the battery fully charged. If you don’t ride often, get a smart charger like this CTEK MXS 5.0 (I have owned one for nearly 10 years now without any issues).
Hook up your battery when you are not riding and let the charger keep it topped up. You don’t even have to disconnect your battery terminals or remove the battery from the bike. Some other things you can do to keep your battery alive:
Don’t leave stuff on
Switch off your engine using the key in stead of the kills switch. That way, all the components are switch off completely and should not drain the battery.
Disconnect when not in use
If you don’t have a smart charger and you are not going to ride for a few days or weeks, disconnect the negative terminal from your battery. This will open the circuit and prevent any draw-down. Unfortunately, the internal resistance of the battery will still drain the battery over time.
It is a good idea to fully charge the battery after standing for a long time. Unlike some riders believe, your alternator (or stator) won’t fully charge your battery, even if you go for a long ride.
Whether your bike will start or run without a battery really depends on a lot of factors, so don’t be surprised if it doesn’t work.
The best advice is to keep your battery maintained and fully charged, and replace it if it is more than two years old (and definitely before a long solo trip into the unknown).