My experience with AAA of any sort is that they tend to be ‘fragile’. It’s easy to charge them too ‘hot/high’. They fail termination more than other cells (end up being overcharged and HOT), and it’s easy to over discharge them, which causes damage. All that contributes to high internal resistance and degradation. I’m in the middle of checking the capacity and resistance on all my battery stock with a theoretically more reliable electronic load tester than the stock analyzing chargers. It does seem to be a lot more consistent. IR for analyzing chargers can be very inconsistent. The higher the IR, the worse the results has been my experience. But, that still tells you something.
My newest/best AAA seem to have an IR of 40-75. The older ones are often 500-900+. In general I’ve seen that the really high IR cells may be the one’s that miss termination, or terminate before being filled, often very soon after being put in. But, I’ve also seen cells with lower IR miss termination. NiMh is simply harder to charge than Li-on. I don’t have any chargers that depend on IR to function.
How fast do AAA go bad? I don’t know. I’m just getting a handle on this myself. I’ll be interested in some other input on this also.