You can blow up batteries, I've seen it done, makes a mess of you and the car. But one other problem is spiking electrics, newer electronics are a bit more robust but you can still do damage. Older stuff you can blow ECUs etc too easily just by connecting or disconnecting leads with the ignition turned on... Other things like connecting leads back to front (only takes a lack of concentration) or one customer that jumped an s class from a lorry and blew every single ECU on it, that cost thousands, (I like to think Land Rover owners are not that stupid) its just something to be aware of. Those situations when you think you've just got a flat battery try to jump it but it still won't go only to discover it's got a knackered ECU! Of course you blame that for flattening the battery but it may have been jumping it that blew it and it was just a flat battery!!! Something to ponder
Sparking at the lead connections is a very high induced voltage, this can travel any where if the circuit is complete ie. ignition on. It's the same reason you're supposed to earth ignition leads if you run an engine with one off! If it can't get to earth the high voltage has to go somewhere, up your arm, thru the insulation, or perhaps down the low tension wires to earth thru the ECU or ignition module, if you're the unlucky one something goes pop. Let's face it tho we've all done it it's only the rare occasion it will happen but it does. That's why you need to be careful. In an ideal world you leave the two cars connected together for the flat one to be able to start on its own. Then turn them both off before you disconnect the leads. Then restart the flat one to charge itself. It applies to either car, you can be the good Samaritan and damage your own just to watch the other guy drive away yes you'd be really unlucky if it did happen but it can, so it's something to bear in mind next time you jump start something if it's got any electronics!

The biggest laugh I remember though was a lad left the keys in the ignition (turned off but still in), when he reconnected the battery it fired up the central locking and locked the car with the only keys inside. That day I learnt how easy it is to pop the locks on most cars. A bit of masking tape, a large screw driver and a length of welding rod was all that was needed for me to get in without leaving a mark.

That was a jeep sales mans favourite trick! Jeep wrangler, record was about 15 seconds

They're gayer than a gaylander, but strangely fun. But I do own a freelander

Of the two, I'd rather have a Freelander. I was toying with getting a Freelander to replace my old van, but something else came up.

if only everything in life was as simple as a subaru driver

Bix said:

Of the two, I'd rather have a Freelander. I was toying with getting a Freelander to replace my old van, but something else came up.

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I got the freelander for a customer whos P38 was off the road over Xmas and new year. She wanted a 4x4 cos of the **** weather we got! Not. We looked at a few most were bags of ****, but this one turned out to be a great little car, so I had it off her when her rangey was eventually fixed!