can you jump start a car from a motorbike?

Most likely not. If the motorbike were 12V it would still be too small for crank amps.

Depends on the depth of discharge on the car. I left the door open on my Ford Explorer in my garage. It just clicked. Used a battery from a cordless drill give me enough boost to start.

If the bike is 12 volt maybe

Maybe. It worn't hurt to try. But if it doesn't work the first time, don't keep trying.

12 volts is 12 volts, some cars start very easily !

We've done it.

Of course both have to be same voltage. You dont wanna try to jump a '63 Bug from a 2006 Harley.

And, depends how many CCA the recipient needs. If simply you left dome light on on a little 4 cylinder car that starts right up if battery charged, you can with a Honda 650 that has its own electric starter, I've done it. Note, the donor motorcycle probably needs to have an electric starter, too, as older 'sickles with kick only often had tiny batteries. ( I did NOT say the starter has anything to do with it, it's just having a starter means a bigger CCA battery .)

Another Thing: Remove jumpers As Soon as car starts. The alternator in most cages can put out 40 amps Or More, the Honda 650 has a 15 amp alternator, at most. The excess current can damage wiring, blow fuse, overheat battery. This is a good rule-of-thumb even if you have a Harley Road King with a beefed up 54 amp alternator...don't risk frying $$ motorbike wiring..

@dr: A 19 Ah Harley battery is bigger than some car batteries. And, it cannot damage the "rectifier". I don't think you even realize what a diode Is. They are rated for a certain reverse voltage; you cannot exceed it by jumping. No current through a rectifier on jumping, anyway. and there are 6 rectifiers, at least 9 diodes., total, Including diode trio and other diodes in the regulator. Only way one could be damaged is reversing the leads, this often blows fuse or fusible link, first, just like in a car. Why do you talk through your hat, no experience?

I knew someone was going to bring up this bullshit. Just like with every electrical question, at least one dead wrong and possibly dangerous answer.

You can try, but it is a bad idea. Those little batteries don't have a lot of current and you risk burning out the motorcycle's rectifier.

No ! But could if you had to. 12 volts to 12 volts the diferance is the starter cranking amps drawn is too much on a car compaired to a small two cylinder cycle batery. Taking a chance of ruining a cycle batery.

I wouldn't try that