My gut tells me rechargeable is better, but only if they are properly disposed/recycled 100% of the time. We don't need more heavy metals in our air/water from rechargeables being incinerated.
Any recommendations for chargers that don't require paired batteries? Some of my recent devices need batteries in 3's and 1's.
Batteries in landfills are pretty inert. None of the heavy metal reactants in a NiMH or lithium cell[1] are ever in a liquid or dissolved state (the charge carriers are hydroxide and lithium ions respectively). One of the reasons they're so pervasive is precisely that these chemistries are safe and relatively non-toxic.
Really, if you're worried about discrete cell batteries and the environment, the solution is to minimize your use of them, not to worry about recyclable vs. not.
[1] Lead acid batteries are an exception, because the sulfuric acid does indeed dissolve some lead. But these really aren't the subject of the article, and in fact they're already being quite effectively recycled in practice.
[1] https://www.globalcitizen.org/en/content/us-landfills-are-fi...
Like the BQ-CC55, it has four independent channels that can charge either AA or AAA in any mix. You can even run different modes on each channel, like charging 1 and 2 while refreshing 3 and 4.
I particularly appreciate how each of the four battery slots is separate. Not only does that mean each battery can be doing something different (charging, refreshing, etc.), it also means you can remove and insert different batteries at different times. This is great when some batteries are more (or less) discharged than others.
Also, worth noting that the BC700 supports NiCd and NiMH, in addition to AA and AAA.
The latter is "put in and forget". The former means fiddling with really bad buttons (because you can! Not really because you have to. But if I can manually set and micro-optimize the charging current, by God I will).
I worry much less about charging nowadays.
IIRC the default behavior is to charge at 200 mA and discharge at 100 mA.
I've had good luck with an Opus brand charger. The one I have allows selecting charging rates (200-1400 mA), and it has an LCD that tells you voltage, rate, status, etc. It also supports some discharge/refresh/test cycle stuff, although I don't know if the practicality of that is real. (If a battery isn't performing right, I feel like it's usually a lost cause.)
I've had a Powerex MC-C9000 [1] that I have used for at least a decade with no problems, mostly with Eneloops. It does not require pairing.
[1] https://www.amazon.com/Powerex-MH-C9000-WizardOne-Charger-An...