As long as a car battery's structure is not compromised or damaged, a cheaper battery poses no more danger than a state-of-the-art one does. Provided the person uses common sense when purchasing or handling car batteries, there is nothing to worry about.
Before installing a car battery, always check for corrosion, broken terminal posts or other damage. The battery works by transmitting electrical current throughout the electrical systems of the vehicle, and loose contacts, corrosion and other physical damage can cause sparks or an explosion if something goes wrong.
If there is a smell like rotten eggs under the hood, it indicates sulfur, which in turn indicates leaking battery fluid. The fluid inside the battery reacts with the metal to produce electricity, and when this fluid is gone it can cause the battery to overheat. If possible, check the fluid levels of the battery regularly.
Buy car batteries only from reputable dealers and physically inspect them before putting them in a vehicle. It's also possible to use a multimeter on the terminals to determine the battery's voltage. Most car batteries operate at 12 volts DC. Over time, this voltage can decrease and not be enough to power a vehicle reliably.