The one thing that I find nicer about the better chargers is that you can be more gentle on AAA cells and charge them at lower currents. The inexpensive chargers that you get free in multi-packs of Eneloops just use the same charge current for both AA and AAA (not that it's going to overcharge either, but the slower charging is supposedly better for the cell lifespan as I understand it, and I'm not usually in a hurry.)
For NiMH cell, there is a possibility of overcharging if its charged with "too gentle" C rate, as charger might miss the termination phase, as the DV/DT signature will be too weak to detect.
I own 2 MH-C9000s since it was released, probably > 5 years now, and lots of Eneloop cells since their 1st generation. All my 1st gen Eneloop with moderate to high usage, all this years, they all charged varies at minimum 0.5C up to 1 C, on average almost all still have >90% of the original capacity, verified using my new SkyRC MC3000 analyzer.
Photo that I took recently on C9000 vs MC3000 size in comparison.
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