Hi, there. A battery is a power supply, a source of potential difference which drives current. In itself, a battery is not a circuit, but if you attach it to a load (a resistance), then a current will form and a circuit is made!
Parallel
no it doesn't if the door is opened when its ON it makes a circuit and starts the car alarm
They are wired in series.
It is a closed circuit if there is a load in the circuit (light bulb etc), otherwise it is a short circuit (+ to - on a car battery with a screwdriver)
No, the battery is part of it's circuit. In fact nothing in the car will work without the battery.
No, it is not normal for a car battery to spark when connecting it. Sparks can indicate a poor connection or a short circuit, which can be dangerous and should be addressed immediately.
have the alternator circuit checked
i believe it would short circuit
Because you won't get a complete and closed circuit without a ground.
A fully charged cell in a car battery produces 2.2 volts, there are 6 cells in a battery. That would make true open circuit voltage on a fully charged battery at 13.2 volts. So a 12 volt open circuit reading is a discharged battery. The battery can have enough chemical reaction to produce voltage but not enough potential or power to crank the engine. Think about a fresh 9 volt battery. It is big enough to produce 9 volts, but not enough to crank a car or even light the dome light dimly. A car battery wears out slowly from the time it is purchased. Eventually it doesn't have enough power or amperage left to operate the car.
The purpose of the battery in a circuit is to wive energy to the circuit
The bulging is caused by gassing. This is caused by overcharging or by a short circuit inside the battery. The acid inside the battery is turned to gas and it expands the sides of the battery.