PLEASE DO NOT connect both your Jumper cables directly to the Battery terminals
I still see people doing this and it makes me crazy.
Always connect one Jumper cable to the positive + terminal on the charged and 'dead' batteries first.
Then connect the other cable to a solid chassis ground as far away from the battery as lead length allows.
There are two main reasons for this (this is 'Auto-Shop 101' but it might enlighten some folks):
Firstly, Lead-Acid car batteries give off highly flammable Hydrogen gas (think Hindenberg) and the spark from connecting the Jumper cable could easily ignite the gas causing your battery to explode. Maybe not a problem with the 'dead' battery, but the charged one could be giving off gas.
Secondly (and less likely), if your battery has died because of an internal short, connecting a high-amp power supply across the terminals is probably a very bad idea and could damage the "good" battery.