2200 means the cells have 200 mAH (milli amp hour) less capacity which is no big deal. NICADs need to be tested under load just like NIMHs. I would not bother trying to replace a partial amount of cells in a multiple packs, use all 12 new cells to build a new pack. The voltage readings indicate all the old cells have been over-discharged. My guess is you would end up with two or more poorly performing packs if you tried to do partial replacements.
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