A battery can be charged in two ways, which can last a maximum of 12 hours. The slow charge, often referred to as the safest technique, requires at least 12 hours to complete the charge and a fast charge is completed in less than 12 hours.
Slow charges make use of a consistent 10-amp current that flows through the battery. Although a slow charge lasts longer than a fast charge, it is considered the safer option of the two.
A fast charge requires a consistent 20-amp current to flow through the battery. Although the constant 20-amps will recharge the battery faster, it poses a chance to accidentally overcharge it and remove it from service.