Charging Time Required

The time required in order to charge a battery will vary depending upon the following factors:
^ Size of battery - A completely discharged, large (heavy duty) battery requires more than twice the recharging time as a completely discharged small (passenger car) battery.
^ Temperature - A longer time will be needed to charge any battery at -18°C (0°F) than at 27°C (80°F). When a fast charger is connected to a cold battery, the current accepted by the battery will be very low at first. The battery will accept a higher rate of current as it warms.
^ Charger capacity - A charger which can supply only 5 amperes will require a much longer charging period than a charger that can supply 30 amperes or more.
^ State-of-charge - A completely discharged battery requires more than twice as much charge time as that of a half charged battery. Because the electrolyte is nearly pure water and a poor conductor in a completely discharged battery, the current accepted by the battery is very low at first. Later, as the charging current causes the electrolyte acid content to increase, the charging current will also increase.

Any battery discharged by parasitic load, and then allowed to stand in this condition for a period of time, may not readily accept a charge. However, if recharged long enough, many batteries will return to a good usable condition.

If the battery remains in an extremely discharged condition for a prolonged period, it can become permanently damaged. This damage can be accelerated by low temperatures. Batteries which are extremely discharged can freeze at temperatures as high as -6°C (20°F) and be permanently damaged.

^ In order to prevent battery damage and recharge problems, vehicles which are not going to be in service within a 20-day period should have the battery negative (-) cable disconnected in order to remove the constant drain on the battery. If this is not possible, the battery should be recharged periodically every 20-45 days until the green dot is visible in the hydrometer or an open circuit voltage of 12.4 VDC is obtained.