The Battery Rating is a factor that shows the battery output performance. The batteries are rated according to the following two standards recommended by the Society of Automotive Engineers (SAE) and the Association of American Battery Manufacturers (AABM):
(1) 20-hour rating (in ampere-hours)
It indicates the lighting ability of a fully charged battery. It is obtained by discharging the battery with a current rate equal to 1/20 of the manufacturer’s rating. It represents the amount of current a battery can give continuously for 20 hours after which the cell voltage should not drop below 1.75V. During the test, the battery temperature should be about 80°F. For example, a 6 volts battery rated at 120 ampere-hours should be able to furnish 6 amperes for 20 hours before it’s terminal voltage drops to 5.25 volts. A battery delivering 5 amperes for 20 hours would be rated as 100 ampere-hour battery (5 x 20 100).
It should be noted that an ampere-hour is the quantity of electrical energy furnished by a current of one ampere for one hour.
It indicates the number of minutes of the 6-volt battery can deliver 300 amperes at 0°F before the cell voltage drops below 1.0 volt. It gives an indication of the cold weather starting ability of the battery.
Sometimes the batteries are rated by the third standard also as follows:
The ampere rating measures the battery performance at a constant current output at 80°F to a final limiting voltage of 1.75 volts per cell. This figure indicates the ability of the battery to carry the electrical operating load (lights, ignition, etc.) when the generator is not operating.
Understand Battery Rating Clearly By watching the video below: