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Comment by hn_acc1 | Hacker News Reader

I did a deep dive into NiMH batteries a few years ago and concluded that most people felt similarly: you can often get "good" (similar to Eneloop) specs for a short run from almost any manufacturer at the outset (see Ikea Ladda batteries - suspected of relabeled Eneloop for a while, but now not as good), but consistent quality is pretty much only Eneloop or other name brand, with Eneloop generally being the best.

In the interests of saving my sanity and time (it's not free!) having to chase down which batch of which brand is "good" at the moment, I just decided on Eneloop all the time. Sure, we now have like 100-120 or something (wife likes flameless candles - just bought another 16-pack AAs) and I COULD maybe have saved $200 by buying dirt cheap. But all the time spent debugging flaky batteries, having the spouse complain, etc wasn't worth it to me (I get paid reasonably well).

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Yeah, name brands like Energizers are consistent but slightly worse than Eneloop at roughly the same price.

I actually made a battery tester as a hobby electronics project. Fully dumps the energy while measuring mAh and seeing some measurements of internal resistance.

Something I did notice was that crappy battery chargers can permanently damage even Eneloops. So don't cheap out on the chargers either.

The high speed chargers (2 hours or less) are on the edge of what is safe and could permanently damage a cell. The 4 hours or slower chargers are just way more reliable. There's probably someone out there testing different chargers (trying to find the safe fast chargers) but given how cheap NiHMs are (even the "expensive" Eneloops), it's just easier to use 4 hour or 8 hour chargers and have masses and masses of extra NiHMs laying around.

I agree about the chargers!

Im sure you know this, but do note that fully dumping the charge can a) damage the battery and dramatically shorten its lifespan, b) give you different results depending on your discharge rate and the batteries you are testing, as they all have different current-dependent discharge curves.

Oh yeah. I stop at 0.95V. which I consider fully discharged (but not so low that I'm damaging the cells). I'm about 10% off the manufacturers claimed specs but I'd rather not push the limits of testing. That's low enough to differentiate between good and bad cells

The discharge rate is currently regulated by only a 2.2 Ohm resistor. The next version of this circuit will be a constant current drain circuit to make all tests draw the same mA across the whole test.

Right now more current is drawn at 1.35V start and far less current is drawn at 0.95V end of test.

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The part that they don't tell you is that 0.95V isn't one point. When you disconnect the cell, it charges back up (kinda like a capacitor). This process can take multiple minutes (!!!!). I've defined the end as being lower than 0.95V for more than 30 seconds, even if disconnected.

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