An automotive battery is a type of rechargeable battery that supplies electric energy to an automobile. Usually this refers to an SLI battery (starting, lighting, ignition) to power the starter motor, the lights, and the ignition system of a vehicle's engine. Automotive SLI batteries are usually lead-acid type, and are made of six galvanic cells in series to provide a 12-volt system. Each cell provides 2.1 volts for a total of 12.6 volts at full charge. Heavy vehicles, such as highway trucks or tractors, often equipped with diesel engines, may have two batteries in series for a 24-volt system or may have parallel strings of batteries.
What size is your battery? What we mean is not physical size, but how many Amp hours does your battery store. As an example, a typical full size auto battery is about 50 amp hours, and it would take a 10 amp charger approximately 6 hours to recharge it if the battery were completely dead. Another example, a Marine Deep Cycle Battery may be rated at 100 amp hours, so it would take a 10 amp charger about 11 hours to recharge a dead battery to near 100% full charge, from a completely discharged condition. To calculate your total charge time, a good rule of thumb is to take the amp hour rating of the battery and divide by the charger rating (amps) and then add about 10% for the extra time to totally top off the battery. Some folks need to size the charge for quick recharge, therefore requiring more amps from their charger. Others are not in a hurry and may select a smaller charger. The most important thing here is to make sure you have enough charger power to do the job you require in the time you allocate.