If we read the owner's manual on the newer cars (I'm old), it will say NOT to connect Positive to Positive and Negative to Negative. We need to ground one end.

I've done it in the past (pre 1990s) it always worked fine. Then some time in 2000+, I've said, this is the last time I would do this. Better start doing it "right."

I've done this again for someone yesterday, and it worked fine.

So why not + to + and - to - ? Is it really that bad?

 

can cause explosion. + of good battery to + of bad battery, - of good batt to bare metal of dead car.

 

The battery can explode. It was always supposed to be done this way. People just did it however it was convenient for them. 9 out of 10 times it may not explode. Do you wanna wait until the 10th time to change your habits???

 

Actually, it can ignite the hydrogen gas produced by the battery. That is the only reason it say not to do that. Doesn't happen very often but it is possible.

 

Right and the battery can explode. There is hydrogen INSIDE of the battery as well as around the posts and vent.