A car battery is a type of electric battery that supplies electric energy to the starter motor and the ignition system of a vehicle’s engine.
They are usually lead-acid batteries that provide a nominal 12-volt (actually 12.6 volt) potential difference.

Types

• The starting (cranking) or shallow cycle type is designed to deliver quick bursts of energy, usually to start an engine. They usually have a greater plate count in order to have a larger surface area that provides high amperage for short period of time. Once the engine is started, they are being continuously recharged.
• The deep cycle type is designed to continuously provide power for long periods of time (for example in a golf cart). They can also be used to store energy from a photovoltaic array or a small wind turbine. They usually have thicker plates in order to have a greater capacity and survive a higher number of charge/discharge cycles.

Use and maintenance

Fluid level

The majority of batteries today are maintenance free and don't require top up. If your battery has easily detachable tops then a top up may be required from time to time. In this case simply remove the tops and top up the cells with distilled or deionised water just above the visible plates.
Tap or rain water should never be used as they both can contain high levels of minerals which will impair battery performance.

Charge and discharge

There are several different methods used to recharge a depleted battery. The most gentle of these is called trickle charging. Other methods include slow-charging and quick-charging, the latter being the harshest.

Changing a battery

In the vast majority of automobiles, the grounding is provided by connecting the body of the car to the negative electrode of the battery, a system called 'negative ground'. In the past this was different, some cars had 'positive ground', but such vehicles were found to suffer worse body corrosion and, sometimes, blocked radiators due to deposition of metal sludge.
When removing a car battery, the ground connection should be removed first and the other connection second. This ensures that a short circuit will not occur by a wrench touching grounded engine parts while disconnecting the other terminal. When connecting a battery, connect the live (or positive) connection first and then the grounded one.

Freshness

You should never buy a battery that is more than six-months old. In the United States, the manufacturing date is printed on a sticker. The date can be written in plain text or using an alphanumeric code. The first character is a letter that specifies the month (A for January, B for February). The letter "I" is skipped due to its potential to be mistaken for the number 1. The second character is a single digit that indicates the year of manufacturing (for example, 6 for 2006).

Terms and ratings

• Ampere-hours (A·h) is the product of the time that a battery can deliver a certain amount of current (in hours) times that current (in amps). Generally that current is baselined at 1 A. This is one indication of the amount of total energy a battery is able to store and deliver at its rated voltage.
• Cranking amps (CA), also sometimes referred to as marine cranking amps (MCA), is the amount of current a battery can provide at 32 °F (0 °C). The rating is defined as the number of amperes a lead-acid battery at that temperature can deliver for 30 seconds and maintain at least 1.2 volts per cell (7.2 volts for a 12 volt battery).
• Cold cranking amps (CCA) is the amount of current a battery can provide at 0 °F (−18 °C). The rating is defined as the amperage a lead-acid battery at that temperature can deliver for 30 seconds and maintain at least 1.2 volts per cell (7.2 volts for a 12-volt battery). It is a more demanding test than those at higher temperatures.
• Hot cranking amps (HCA) is the amount of current a battery can provide at 80 °F (26.7 °C). The rating is defined as the amperage a lead-acid battery at that temperature can deliver for 30 seconds and maintain at least 1.2 volts per cell (7.2 volts for a 12-volt battery).

Reserve capacity minutes (RCM), also referred to as reserve capacity (RC), is a battery's ability to sustain a minimum stated electrical load; it is defined as the time (in minutes) that a lead-acid battery at 80 °F (27 °C) will continuously deliver 25 amperes before its voltage drops below 10.5 volts.  A value close to 1 indicates a well-performing battery with little loss. A higher number reflects a less efficient battery.

• The open circuit voltage, measured when the engine is off. It can be approximately related to the charge of the battery by:

The following is common for lead-acid batteries:

• Open-circuit voltage at full charge: 12.6 V
• Unloading-end: 11.8 V
• Charge with 13.2-14.4 V
• Gassing voltage: 14.4 V
• Continuous-preservation charge with max. 13.2 V
• After full charge the terminal voltage will drop quickly to 13.2 V and then slowly to 12.6 V.