Internal short in the lead plates, time for a new battery.
No, a car battery does not have mercury in it. It would be very dangerous to have mercury in a car battery.
if you have smoke coming from your battery then the cause sounds like a dead short the possble pop you heard would be one of the major fuses,not the tiny ones. you may have a cable rubbed through,or other major wiring fault
I suggest you buy a new car battery replacement in http://www.laptops-battery.co.uk/.
It's not healthy, but yeah. The trouble with a charging battery is hydrogen buildup from lead-acid (car) batteries.
Without a battery to work an automobile then the car would not get anywhere. The battery helps to run the car with moving all the parts that would be required to drive.
Once the smoke escapes you cannot put it back! Seriously, though, Make sure that the Ground is connected to the chassis/solid grounding point and not the battery, make sure the donor car runs for a minute or two while connected before attempting to start the dead car. Also helps to increase the RPM of the donor car while cranking the other.
It would vary from car to car.
You would make a car battery comparison by comparing which car battery seems better. You shouldn't keep the old car battery near because you can get it mixed up with the newer ones.
Car should be OFF. If it CAN be refilled you would remove the caps located on top of the battery. Carefully add distilled water until water level is full but not overflowing. Replace caps. Wipe off any spilled water. Do NOT get any water from battery on your clothes, skin or eyes. Do NOT smoke while refilling your battery - it could explode!
If your car has a battery and it's dead, you can call a friend who has some jumper cables. You can hook the jumper cables up to his battery and your car's battery. It should create electricity that will renew your battery. If your car does not have a battery, you would have to push it or get it towed.
The battery needs to be replaced
If you are using it to turn on the car a good battery would help.