Home » GM 6.5 » GM/Detroit 6.5L – BATTERY RATINGS


A battery has two ratings: reserve capacity and cold cranking amperage.

Reserve capacity is an estimate of how long the vehi­cle can be driven with no generator output, the head­ lamps turned on, and minimum electrical load (most accessories turned off). It is the maximum amount of time (in minutes) it will take for a fully charged battery, being discharged at a constant rate of 25 amperes and a constant temperature of 27° C (80° F), to reach a ter­minal voltage of 10.5 volts. Other temperatures or cur­rent draws, the state of charge, the condition of the battery, etc., will affect how long the battery will actually last when the vehicle is being driven and there is no generator output.

Cold cranking amperage is an indication of the ability of the battery to crank the engine at cold temperatures. This rating is the minimum amperage the battery must maintain for 30 seconds at -18° C (0° F), while main­taining at least 7.2 volts. The actual performance of a battery will vary with actual temperature, etc.


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