Hot cranking amperes:
Hot cranking amperes refers to the amount of current the battery can deliver at 26.7 °C. The rating defined as the current in the battery at the temperature. The load need to deliver the cracking amperes for 30 seconds and currently maintained at 1.2 volts per cell. When a battery drops below 10.5 volts the plates are damaged.
Royal 56637 Semi-Sealed Maintenance Free Battery
Reserve capacity minutes:
Reserve capacity minutes refer to the minimum current the battery must deliver 25 amperes before its voltage drops below 10.5 volts. If the volts drop below 10.5 volts during the reserve capacity the battery should be charged.