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Testing capacity of Calb 180ah cells

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I purchased some of these cells used and want to test the individual capacities before I build them up as a pack. The spec says that they are rated at 180ah @ .3C

So that would be 180 * .3 for a 54 amp load. Can I just use a power resistor (around .05925 ohms) to achieve the 54 amp load and count then time until the cell hits 2.5 volts? Should be around 3 1/3 hours. Do I need to be taking into account that the voltage will be dropping during this test? Should I be counting watt hours instead?

I know I could use a amp meter, but I want to understand the principle behind the test. Thanks!