So you’re stepping off the front porch on your way to work. You hop in your trustworthy 1969 Mustang Boss with the 429 cubic inch engine, turn the key only to find out the battery is dead. Thankfully, your neighbor just happens to be a motorcycle gang member, and he has a battery, but will it work in your car?
A motorcycle battery will work just fine for jumpstarting a car in most situations. However, there are some variables to consider, such as the size of the vehicle compared to that of the bike, how cold the weather is, and if the bike’s battery is healthy enough.
Admittedly, those are some heavy variables. But I stand by my claim that chances are, a motorcycle battery will do the trick in a tight pinch. To understand why this works—or in rare instances, doesn’t work—let’s examine jumpstarting in general and the differences between car and motorcycle batteries.
Jumpstarting 101
Jumpstarting is the act of creating a current between a weak battery and a strong one. The weak gains cranking amperes from the strong, enabling it (in theory) to start an engine. Four jumper cables are attached to the batteries to create the current. Each cable has a clip for each battery terminal.
In this case, the external supply of energy, the motorcycle battery, provides the power needed to crank the dead car battery. Once the car starts, its regular recharging system will recharge the dead battery.
So long as the source battery is strong enough and you follow the correct procedures, a successful jumpstart is all but guaranteed, even with a motorcycle battery.
Car Batteries and Motorcycle Batteries—The Differences
Car batteries and motorcycle batteries look good together. They are different but the same. I didn’t just pull that out of a Chinese fortune cookie. Instead, experience in motorsports has taught me some truths.
Breaking down the contrasts here in a simple fashion, we’ll consider:
- Size
- Voltage
- Cranking Amperes
A car battery weighs about 40 pounds (18.14 kilograms), whereas a motorcycle battery tips the scales at just over 5 pounds (2.27 kilograms). Based on those numbers, you might be thinking: come on, man—there is no way a bike battery will jumpstart a car.
But really, it isn’t about poundage. Both those averages I gave? The former produces about 12.6 volts; the latter clocks in at an even 12 volts. A healthy 12-volt battery can and will jumpstart a car.
Voltage is how the difference in charge between two points—for instance, a battery’s positive and negative terminal—is defined. This difference is also known as electric potential. Connecting the positive and negative terminals forms a current of electricity through the car (or motorcycle).
The strength of these currents is defined through amperes, which is the subject we’re going to examine next.
About Cranking Amps
Cranking amperes, or CA, will tell you a battery’s ability to start a vehicle in normal climate conditions (a climate where the temperature rarely, if ever, dips below freezing). Over a span of 30 seconds, the battery should be able to turn the vehicle’s engine about once per every cubic inch of the engine.
For example, with Mustang Boss’ classic 429 cubic inches (7.03 liters) engine, her battery should be able to crank the engine at least 429 times in the space of 30 seconds.
Now, most of today’s engines aren’t anywhere near that big, so don’t necessarily worry about your motorcycle’s tiny 12-volt battery not having enough juice for a jump.
To give another example: Your average 1.6-liter engine contains about 98 cubic inches. A 3-liter V6 engine has something more like 181 cubic inches. They just don’t make ’em like the Boss anymore.
Does My Motorcycle Battery Have Enough Amps To Jumpstart a Car?
The previous section may have left you wondering whether or not your bike’s battery can jumpstart your car. It is entirely possible if your motorcycle has a battery over 12 volts that is in good condition.
Your motorcycle battery will have enough amps to jumpstart a car if the bike has a 12-12.6 volt battery. It takes about 200 amps to start a motorcycle and around 450 amps to start a car. A motorcycle battery can jumpstart your car because both your bike and your car likely use 12-12.6 volt batteries.
If you’ve got a dead car battery that needs a jump, and your neighbor’s big Harley is looking like the only beast around that can help, you can skip to the how-to section below. However, if it’s cold outside—like below 0℉ (-17.78℃)—you may wish to look at the next section about cold-cranking amps.
About Cold Cranking Amps
If you live in the north, you likely understand that starting a vehicle in warm weather is much easier than in the colder months. Indeed, I would need an abacus to tell you how many frigid Ohio mornings I wound up walking to school because my dad couldn’t get his poor old Galaxie 500 to start. So how does this sad anecdote relate to cold-cranking amps?
Cold-cranking amps, or CCA, define a battery’s ability to start in cold weather. The most basic way to put it when speaking of cold weather is to use the example of a 12-volt battery at 0℉ (-17.78℃). That’s cold enough to freeze nostril hairs or get your tongue stuck on a light pole.
Remember that we’re still talking about how many times the battery can turn the engine in 30 seconds. If your neighbor is crazy enough to ride in sub-zero weather (and if you can get his big beard out of the way), the CCA of his battery will likely be enough to jumpstart your car.
All right, so I’ve told you it could be done. But I haven’t told you how yet. That part comes now.
How To Jumpstart a Car With a Motorcycle Battery
The process of jumpstarting a car with a bike battery is relatively straightforward, providing you follow the correct procedures. Having a rider rev the motorcycle engine is a great advantage as the increased revs produce a stronger current of around 13.5-15 volts.
This excess charge could make the difference between a successful jumpstart and an unsuccessful one. So if it is possible, try and find a rider to help you jumpstart your car rather than just rely on the motorcycle battery
To achieve the best results, you should follow these steps when jumpstarting a car from your bike battery.
- Roll the bike up next to the car.
- Pop the car’s hood and make sure the battery is easily accessible.
- Connect the jumper cable’s positive clip (red) onto the bike battery positive terminal.
- Connect the jumper cable’s negative clip (black) onto the bike battery negative terminal.
- Fire up the bike WITHOUT letting the opposite clips of the jumper cable touch each other.
- Connect the red opposite clip (positive) to the car battery’s positive terminal.
- Connect the black opposite clip (negative) to the battery’s negative terminal.
- Let the bike run with everything connected for about ten minutes.
- Try to start your car.
In a perfect world, the car will start. VROOM! Now you need to hop out and disconnect the car battery from the bike. Don’t let it run connected for too long—this is because the current from the car will eventually become stronger than that of the cycle and could damage the bike’s electrical system.
As frustrating as it seems, despite your best efforts, the car will not start. From this point, you have two choices: let the bike idle for a few more minutes and try again, OR…
Get a buddy to rev the bike’s engine to about 4000rpm, which will produce a stronger current. While your buddy revs the bike engine, get in the car and try to start it. And remember that if the vehicle does start, get out and disconnect the cables. Congrats, man. Your day just got a little bit better.
Can I Jumpstart Without the Motorcycle? (Just the Battery)
I’ll note that sometimes firing up the motorcycle before a jumpstart isn’t an option. Many bike batteries are housed under the seat, making the terminals challenging to reach. Now what?
You can jumpstart without the motorcycle and just the battery if it is strong and in good condition. The newer the motorcycle battery, the better chance you will have a successful jumpstart of a car. It also helps if the bike battery has high cranking amperes.
Note that I said it can, but not definitely will. Jumpstarting a car with a removed motorcycle battery is akin to tip-toeing through the tulips to the music of Tiny Tim. It’s strange. It’s delicate. And it takes luck not to fail. I honestly wouldn’t attempt this unless the motorcycle battery is either new or like new.
If you are attempting a jumpstart of only your motorcycle battery, it will probably only work in certain instances, such as when the car engine is warm or your car does not have a large engine system.
If you’re in a bind and decide to try, hook everything up as described in the previous section. Then give the car a 5-10 second crank. Wait two to three minutes and try again. Don’t crank the car engine for too long, as all that’s going to do is drain the poor motorcycle battery.
When NOT To Try a Jumpstart
After reading the above material, you might be feeling pretty good about motorcycle batteries jumpstarting car batteries. And I’ll state it here yet again—it works. Still, we have got to consider the caveats. There are some instances where a jumpstart really shouldn’t be attempted.
Forgo all thoughts of hooking a bike battery up to a car battery if:
- One or both batteries are bad (bad batteries often smell bad or won’t restart a vehicle even after you just shut it off).
- The motorcycle battery is old, damaged, or is only 6 volts.
- Your jumper cables are damaged.
It’s also worth noting that modern cars come equipped with multiple electronic control units (ECUs).
These units have delicate dispositions about electrical surges from external sources. If your car’s check engine light comes on after a jump, please have a qualified mechanic check the ECUs.
What About Jumpstarting an Electronic Vehicle (EV)?
It isn’t often that one of today’s modern electronic vehicles needs a jumpstart, but it can happen. If you find yourself with an EV with a flat battery, you could consider jumpstarting the vehicle from a motorcycle battery.
You can jumpstart an electronic vehicle (EV) the same way you can a regular gas-powered vehicle. This similarity is because a lot of EV units use a standard 12-volt car battery to power components such as lights, the radio, and the HVAC.
Most electric vehicles come with two batteries—a big one to power the motor and that smaller 12 volt to power everything else, including start-up. Rarely will the 12 volts die, as it gets its charge from the larger battery (and not from, say, an alternator the way gas cars do). You can indeed jump it from a motorcycle if it does die, following the same instructions seen above.
Never attempt an EV jump while the EV is plugged into another charger. The 12 volt must do its work alone. Plugging in the EV while trying a jump could and probably will create an unwanted electrical surge.
Conclusion
Your motorcycle can jumpstart a car, provided the motorcycle battery has good cranking amps and is at least 12 volts. Most vehicles today also use 12-volt batteries, so that is the number I’ll use. I advise it only when necessary.
The bike’s electrical system isn’t as large or accommodating as a car’s. An anomalous surge could damage the bike if you’re not quick with disconnecting the cables after the vehicle starts.
But enough tech-talk. How do I know a motorcycle battery can jumpstart a car? I’ve done it myself. Scout’s honor. Trust an old man on this one.