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Cells in a battery

  1. Apr 22, 2009 #1
    Hi,

    Im looking for a new laptop battery.

    Something thats confusing me is the number of cells in a battery; what is a cell? is it a smaller battery that exists in the larger battery?

    If so, are the cells connected in series whose voltage sums to the voltage of the total battery?
    Or are the "cells" connected in parallel...for reasons I can only guess at?

    Also, and more to the point I am trying to figure out: I know laptop batteries are rated in mAh, how much charge it can hold. But would it be better to get a 12 cell battery or a 9 cell battery, both with the same charge capacity?

    My intuition would be that fewer cells would be better because the lifetime of the battery will be longer: Since the internal resistance of the battery builds up in each cell, there will be less internal resistance if there are fewer cells (since they are in series).

    Here I am assuming that all the cells, whether they are in a 9 or 12 cell battery, develop internal resistance at the same rate; which I dont know if is true.

    Thanks for any help
    Raman
     
  2. jcsd
  3. Apr 22, 2009 #2
    A fully charged lithium bettery cell has a voltage of about 4.2 volts. The bigger the area of the cell, the more amps it can provide. Put 3 cells in series and you have a 12-volt battery. Put 3 cells in parallel, and you have a 4 volt battery that can deliver the same current 3 times longer.
     
  4. Apr 22, 2009 #3

    mgb_phys

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    In other words - if you have a choice of batteries for the same laptop the battery life will be proportional to the number of cells. A 12cell will last 1/3 longer than a 9 cell

    This isn't necessarily true between different laptops - the cells might be different.
     
  5. Apr 22, 2009 #4
    Will this be the case even if the 12cell and the 9cell have the same charge capacity? The 2 im looking at both can hold 7200mAh, but one is 9cell and one is 12cell.
     
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