There is a thread in here about how to test the internal resistance. You can sometimes determine the health of your cells this way. First things first, though, check those voltages! Chances are you will find one or three cells with much lower voltages than the others. Recycle those, they are no good.
Please also be careful disassembling these. The bus bars are flexible and can contact your metal tools, shorting out batteries. You don't want to be around a battery that has been shorted out for a long time.
As for IMRs, if you search hard, you will find some power tools that contain IMR18650 cells. Others may only contain LiFePo4 A123 cells. If you divide the total voltage by common Lithium Chemistry voltage, you can get an idea of how many cells there are. In series, voltage adds up, capacity doesnt. In parallel, capacity adds up, but voltage doesnt.
example: 5200mAh 11.1V battery pack is assumed to be made up of 3.7V cells. 3 in series gives you 11.1V, but no 18650 has 5200mAh, so there must be two strings of three 2600mAh 3.7V cells.
An indication of IMR cells is generally a lower than expected capacity. Closer to 1500mAh.
Cells with that pink wrap are made by Sanyo Electric Co., and are good sauce! I lucked out, harvested 9 sanyo 2600mAh cells with less than 50 total cycles, as recorded by the battery pack. These are the same cells LarryDFW sells (He sells these cells by the seashore), BUT his are new, and as such, will actually have the capacity that they are rated at.
On a side note, you will notice several thermal sensors, a thermal circuit breaker, and some fancy circuitry. This is what keeps these batteries safe. Those ICs retain information about voltages, cycle counts, bad cell locations, etc., and keep the pack running smoothly. A lot of work goes into protecting these cells. Much less work goes into making our hobbiest-grade protected cells.
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