+1. The issue is not the lead polarity but connecting the jumpers to the battery terminals and not a ground source away from the battery.

 

I connected the negative to the spare tire bracket. I also thought of connecting to hood latch on the hood.

Thanks for the responses. I knew enough not to put negative to negative.

 

Interesting...

 

Always connect the weak battery (the one generating the gas) first and in this order:
Isolate the cable ends going to the jumper battery (have someone hold them apart).
Connect the cable ends to the weak battery terminals.
Connect the cable ends to the jumper battery.
Using this method there is no possibility of a spark when connecting to the weak battery terminals as there is no circuit being completed when connecting.

If there is accumulation of hydrogen gas at the weak battery, connecting to a ground a few inches away will provide little if any explosion protection. Also most modern cars do not have exposed bare metal to connect to, so connecting to a poor conductor may infact cause sparking when trying to start the car.

Mike