This post explains why it's a potential hazard to clip to the negative post on the dead battery when giving a boost. But I've also been told that I could damage the electronics in my own car if I give someone a boost or do it "wrong".
Is this really the case? What are the circumstances that this could end badly for my car?
You can get transient spikes from the other car while it's trying to start. Any battery or alternator issues that affect power quality will be transmitted to your car. The good news is that large 12v batteries make excellent buffers against power issues that might otherwise cause damage. However, it is still possible to suffer damage to your car from jumping someone elses. Pretty rare though, doesn't make my list of things I worry about. :-)
I can't think of any reason why you would damage the electronics in your car, unless you touched one of your jump leads somewhere you shouldn't and short something delicate or you connect the leads back to front.
Connecting them back to front shouldn't damage electronics, as your car should have protection against this sort of thing, but it is the key thing to check - just in case.
An example I can think of might be - an aftermarket car stereo may not have surge/voltage protection and it may be connected directly to the battery, not through the ignition switch, so connecting 12v across it the wrong way may damage it. More realistically it may just blow a fuse or a diode.
As commented below, this could damage batteries - I was purely talking about electronics. Look out for your batteries :-)
Answer is yes yes yes to damage. Some guys borrowed my car to jump-start another yesterday. They mixed up the pos/neg connection and my car died a sudden death. I have just phoned my mechanic who said it will have damaged any number of things/fuses/electric systems. I am currently waiting for the AA to come and jump-start the car so I can drive it to the mechanic. I am not at all looking forward to the bill and really annoyed @ the guys. :(
Yes, it is possible to damage either or both of the cars. There's a risk of serious overvoltage when jump-starting and that can damage any electronic equipment and even headlights that are on during the procedure.
That's why, for example, Ford Focus C-Max manual says that all electronics and headlights should be turned off during the jump start.
