You can now find 1.5V Li-on AA batteries with, and that's a game changer, built-in charger and a type-C port!

I have one in my wireless mouse. If it dies, I change it to a spare and charge it right from my laptop (and the battery that was empty becomes the spare)

I believe I have zero Alkaline batteries left in my house and I'm relatively surprised that pretty much everything works fine. If anything, I suspect the only problem is that some devices have an inaccurate account of how dead the batteries are. But I use Eneloops on everything, even things surely not designed at all to run on them. (And I reckon you could probably make more devices work if you really wanted to; adding an additional cell or two in series would surely give you a voltage that's in range, if you can figure out a good way to do it.)

Of course not all rechargable batteries are the same; there are a few different rechargable battery chemistries in the AA form factor. I like Eneloop Pros, though; they've been very reliable for me. I've been using them for years and I've never had to throw one out yet; supposedly they last over a thousand cycles with most of their capacity.

That's not the reason.

Alkaline batteries only have 1.5V for a short time. In practice, toys are designed to opeerate off of 1V to 1.5V, because Alkalines vary _wildly_ in voltage during use.

NiMH at 1.2V _STAYS_ at 1.2V, even when drawing 1Amp or more (under these conditions, Alkaline would have long dropped below 1V).

EDIT: This is also a problem because "nicer toys" will measure the voltage assuming an Alkaline is "full" at 1.5V and dies at 1.0V. However, NiMH starts at 1.35V, then "plateau" at 1.2V, and stays there for most of its life, before rapidly falling off to 1.0V or .8V like a cliff at the end of its life. So NiMH life "cannot be predicted" by any simple metric.

If they don't work at 1.2V they weren't very good quality to begin with. AAs are dead at 1.0 or 0.9V.

There are a lot of low–quality toys.

A weird flipside is things like... the IKEA Zigbee devices. Many of these do not work right at all with 1.5V batteries and basically require rechargables.

NiMH chemistry allows for safe overcharging though. If the chemistry allows for it, why not take advantage of it and have cheaper chargers?

The downside is that "save overcharging" only works at very low charging rates. That's why the double-charger designs all have 10+ hour charge times (mine actually has a 20-hour charge time).

But in practice? Its cheaper to buy 4 extra AA NiMH batteries to keep charged rather than upgrade to the faster chargers. So just keep some spares topped off and you should be fine.

Series X controllers still work this way. Takes standard-ass AA batteries, including rechargeables; or you can buy a bespoke charge pack[1] which actually supports charging while in the controller.

[1] https://www.xbox.com/en-US/accessories/batteries-chargers/pl...