Fact about maintenance-free battery of car

Nowadays, most car battery is a lead-acid storage electrochemical device that can converts chemical energy into electrical energy. A standard 12-volt, lead-acid battery is made up of 6 cells connected in series. Each electrolyte filled cell produces approximately 2 volts. The charge of this 12-volt battery is actually at 12.6 volts, and can vary slightly depending on the concentration of the electrolyte in its acidic solution.

The "maintenance-free" battery, similar in design to its conventional counterparts that need to refill with distilled water from time to time to maintain the fluid level, is actually just a heavier-duty version of the same arrangement. Many of the components in the maintenance-free battery have thicker construction. Different, more durable materials are typically used. For example, the plate grids often contain calcium, cadmium or strontium, to reduce gassing (which causes water loss) and self-discharge. This design is called a lead-calcium battery. The heavier-duty parts ensure that fluid loss is kept to a minimum and that components have a much longer life, making it a closed system.

The advantages of maintenance-free battery are: less preventative maintenance, theoretically longer life, faster recharging, greater overcharge resistance, reduced terminal corrosion and longer shelf life. However, they are more prone to deep discharge (dead battery) failures due to increased shedding of active plate material.