From: ehsjr@verizon.net   
      
   On 9/20/2019 6:14 PM, AK wrote:   
   > I want to calculate approx run time of a D cell with a capacity of 13,000   
   Mah.   
   >   
   > I assume that Time(H) = Capacity(Ah)/Current(A) equals a final battery   
   voltage of 0 volts which will not work in my case.   
   >   
   > I need a calculation for an ending voltage of around 2.0 volts.   
   > (At 2.0 volts, my clock starts losing time.)   
   >   
   > Thanks   
   >   
      
   I assume you have two D cells in series, since you specify an ending   
   voltage of 2 volts. A single D cell provides 1.5 volts.   
      
   Generally speaking the mAh discharge voltage for a single D cell would   
   be around 1 volt, not 0 volts, but that doesn't matter too much.   
   Read on.   
      
   The equation will give you ONLY an approximation.   
      
   The rate at which a battery discharges varies with the amount of   
   current drawn. Unless the load is designed to draw constant current,   
   the denominator (Current) in your equation is a variable so you   
   can't solve it accurately.  Add to that the fact that the discharge   
   rate is not linear even at constant current, and you can see the   
   difficulty with getting a precise and accurate answer. Look at   
   some battery discharge curves to get a feeling for this.   
      
   Ed   
      
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