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50 Amp Hour Battery

  1. Mar 14, 2009 #1
    Hi I was using a 50 amp hour battery and running something which is using 2 Amps all the time..

    How would I calculate the time the battery will last ?

  2. jcsd
  3. Mar 14, 2009 #2


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    Staff: Mentor


    ...but depending on the type of battery, 50 amp-hours may not really be 50 amp hours and 2 Amps may not really be 2 amps. These things change as the battery discharges, so depending on how accurate you want to be, you may need to account for them.
  4. Mar 14, 2009 #3
    If life was only that easy!
    You need to get the battery data sheet which will give you the data.
    Battery discharge graphs are curves and are not linear therefore you cannot simply divide 50 by 2 to get 25 hours.
    The battery you mention is 50Ah but at what C rating is this? For example if the battery is 50Ah at C5 then it will give 50Ah for 5Hours ie 10A per hour. This does NOT mean that you can then say it will give 50A for one hour or 1A for 50 hours.
    You will also need to know how low you can allow the battery voltage to drop. All battery discharge data is given down to a specific voltage. For sealed lead acid batteries this is usually down to between 1.6-1.9 V per cell.
    If you get the battery manufacturer and model then you should be able to search online for the battery discharge data sheet.

    Last edited: Mar 14, 2009
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