Originally Posted by
nbTMM
As far as internal resistance goes, it does not reduce the actual capacity of the battery ...
Unless your packs have a wildly different internal resistance AND you're drawing stupid currents almost constantly, it will therefore be a non issue ...
If you buy two packs at the same time, same manufacturer and model, then both the capacity and internal resistance should be quite well matched...
Consider the following article:
Originally Posted by Battery University
A manufacturer cannot predict the exact capacity when the cell comes off the production line...
As part of quality control, each cell is measured and segregated into categories according to their capacity levels....
Adding cell balancing is beneficial especially as the pack ages and the performance of each cell decreases at its own pace...
A battery expert once said: “I have not seen a cell balancing circuit that works.” For multi-cell packs, he suggested using quality Li-ion cells that have been factory-sorted on capacity and voltage..
With use and time, battery cells become mismatched...
My take on this article is that it only discusses matched cells in a single pack, they explain how the cells are carefully grouped together when they are matched. It would be a bad assumption that 2 packs from the same manufacturer are matched, in fact you would have to be extremely lucky to get 2 matched packs at random... perhaps it might be possible to get 2 matched packs, but that would require you to use the same method that the manufacturer used to match the cells in the first place... this would not be practical which would require you to keep buying additional packs until you eventually find a matched set.
Another article here worth a read:
Originally Posted by Battery University
All batteries age and the effects manifest themselves in diminished capacity, increased internal resistance and elevated self-discharge.
So the relationship between IR and capacity is through age in how they are directly related.