Lifted from a BMW forum I frequent.....................
Best practice is to connect the jump leads from donor to casualty first, this way you wont shock either vehicles ECM's,
Start the donor vehicle and let this charge the casualty vehicle for 15 minutes, At this point the casualty's battery will have sufficiant charge not to drain from the donor, do not remove the jump leads whist the vehicles are running as an amp spike may harm ECM's on either vehicle,
Once they have both run for another 10 minutes, switch both vehicles off, now you can remove the leads, if the casualty vehicle does not start then its time for a new battery, if it starts then get the battery checked as it may only hold a surface charge,
start the donor vehicle and run for 15 mins to recharge the battery,
An alternator is not designed to charge a wet cell batttery from flat, the levels are brought up too fast and this can damage the battery if not already knackard, A trickle charge may recover a dead battery but is not always a given, Always check that the alternators output is within spec, both voltage and amps,
and for those who dont know,,,, red is positive and black is negative, lol
RAC patrol manager
Dave
