Post the year, make and model of the vehicle (in new question) and one of us can tell you if it is negative or positive ground.
MY VEHICLE IS Ford Fiesta AUTO, year 2016. could you please tell me,
is it negative or positive-ground
You will damage the electrical system of the car
On the car battery, the positive wire is red and the negative wire is black. If the body of the car is metal or conducts electricity, then the body of the car serves as the negative wire. The metal in the engine serves as the negative wire.
If you have a post battery(the cable attaches from the top) the positive post is larger than the negative.
Find the cable that is connected directly to the frame or sub-frame of the car. If it is red, then Positive is ground; If it is black, then Negative is ground. More than likely (but not in all cases) the electrical system is Negative ground.
You conect them in parelell. Positive to positive, negative to negative, with either a 12 or 6 volt system. if you conect them in series you will double the voltage.
NO! positive is red and black is negative negative is grounded to the frame of the car, and positive goes to the electrical components.
If you want to jump start your car, connecting negative to negative and positive to positive is the only way to do it. Connecting negative to positive will result in extensive damages to the electric systems of both cars.
It is almost always imprinted on the battery next to the posts. If not the positive + post is slightly larger than the negative - post.
The center is the positive.
A small spark is normal, it is energizing the system.
Cause the battery to explode or damage the electrical system in the car.
You could put them in parallel--wire positive to positive, negative to negative, then connect the positive and negative wires to the car. This would give you twice the current capacity, and you'd be okay because the car's only going to take as much power as it needs. If you wired them in series--positive on the first battery to the car, negative on the first battery to positive on the second, negative on the second battery to the car--you'd double the voltage and burn the car out.