Its got nothing to do with the battery blowing up, its to do with the car's computer electronics. Battery to Battery leads to power spikes which upsets the car's electronics.
It may not happen every time, but when it does, its going to be expensive.
I would not want to be the bearer of bad news to a car owner for being the one responsible for detonating his electrical system.
This system eliminates the possiblity./
By changing the setup from battery to battery to earth points is going to make absolutely no difference to the chance of a voltage spike that could damage the computer on either vehicle.
As correctly stated by others the emphasis on the
final connection to an earthing point is so that a spark wont be made at the battery where there is the potential to ignite generated hydrogen. Id consider the risk of this miniscule in open places, where any hydrogen produced quickly rises or that significant amounts arent created until the system has been charging for a while anyway.
There are other advantages to making the connections away from the battery in the car being 'jumped' By making the jumper connection direct from the donor battery terminals to the +ve of the starter and a good earth on the engine block, the circuit effectively becomes ~ 2m shorter and there will be more voltage available at the starter, which could make the difference(especially with limited contact available through clamps) to actually get the starter to turn fast enough.
Many report here that they have no troubles with jump starting their ecu cars, either have I, however, that doesnt mean that damage to the ecus can not occur and is certainly not unknown. Perhaps spike protected leads would be a prudent choice.
Some other things I do/dont do:
1. Dont have ignition/enigne running on or any other accessories when connecting between the vehicles. This minimisese the voltage difference when connecting, which could be a source of a spike.
2. If time is available, start the engine of the donor vehicle and run it at 2000rpm for a couple of minutes or so. This will start to charge the battery of the other car, if its simply discharged. Even a couple of minutes of charging through a high powered car alternator could give the dead battery all it needs and/or make the subsequent jump start much easier.
3. When attempting to start the dead car, turn off the ignition of the donor car. This will again minimise any electrical spikes that could affect components on the donor car and a potentially damaging load on the alternator. Many like to keep the motor running on the donor car in fear that they may drain their own battery. If after 20 secs or so of cranking the dead car wont start, restart the donor car and charge up the battery for a couple of minutes before reattempting.
