The reserve capacity is the time in minutes that a new, fully charged battery can be continuously discharged at 25 amperes and maintains at least 1.75 volts per cell (10.5 volts for a 12-volt battery).

Minutes discharged at 50, 25, 15, 8, and 5 Amperes
Minutes discharged is the time in minutes that a new, fully charged battery will deliver at various currents and maintains at least 1.75 volts per cell. These are nominal or average ratings.

Ampere Hour Capacity at 20, 10, 5, 3 and 1 Hour Rates
Ampere hour capacity is a unit of measure that is calculated by multiplying the current in amperes by the time in hours of discharge to 1.75 volts per cell. These are nominal or average ratings.

Examples
    5 amperes for 20 hours (5×20) = 100 AH @ the 20-hour rate
    10 amperes for 3 hours (10×3) = 30 AH @ the 3-hour rate
    20 amperes for 1 hours (20×1) = 20 AH @ the 1-hour rate
  Therefore, if you have am application that requires a draw of 15 amperes for 5 hours, you would need a 75 AH battery (@ the 5-hour rate).

Examples
    5 amperes for 20 hours (5×20) = 100 AH @ the 20-hour rate
    10 amperes for 3 hours (10×3) = 30 AH @ the 3-hour rate
    20 amperes for 1 hours (20×1) = 20 AH @ the 1-hour rate

Ampere hour capacity is a unit of measure that is calculated by multiplying the current in amperes by the time in hours of discharge to 1.75 volts per cell. These are nominal or average ratings.