Newbie Question on NiMH batteries from Cells of vastly different capacity

[mudgluttentoo]

Hi,

my first posting and perhaps a numpty question, but here goes...

I have a battery of 14 x 2,600 mAH NiMH AA cells, that has plenty of capacity but is short on voltage. If I add a PP3 style 800 mAH battery, that gives me a further 7 cells of 1.2V / 114 mAH each and 25.2V terminal pd overall. However, as the cells within the pp3 are each less than 5% of the power of the AA cells, will they discharge in the drop of a hat, or over the same period as the rest of the cells in the battery?

Thanks.

 

[Mr Happy]

To correct your original wording, the cells in the PP3 have less than 5% of the capacity of the AA cells. This means they will indeed be discharged in the drop of a hat, and soon after the 9 V battery will be destroyed by reverse charging. (It's like connecting a thimble in series with a bucket. How soon will the thimble be emptied if you empty both at the same rate?)

When you assemble a pack, it is important that all cells in the pack have the same capacity, and also that all cells in the pack are kept balanced during charge and discharge so they keep the same state of charge.

Incidentally, if the 9 V battery is 800 mAh, then each of the cells is also 800 mAh. But that seems like a very high capacity for a 9 V PP3 battery. Are you sure about that?

 

[jhellwig]

So....are you wanting to make a pack with 9v and aa batteries?

 

[mudgluttentoo]

Sorry to be so late in replying - screening delays etc. Er. no, I won't be adding a PP3!