I really think Nintendo should take this idea, dump the AA battery part, put a standard 2200 MaH ion-lithium battery on both sides let the base Switch 2 have access to that extra juice. You could use it to either battery boost (double the battery life) OR allow Switch 2 to run at docked clock speeds even when undocked (performance boost).
And these things have a nice bonus in making the Joycons more comfortable to grip too, you could probably tweak this design to be even more comfortable.
3-4 hours is good enough for me, but I'd like to be able to run full performance (12-15 watts) while on the go. It's a simple idea, but I think it would help the Switch 2 hardware a lot.
It'd be effectively three batteries for the Switch 2, which in unison could give it a bigger overall battery to draw on than the Steam Deck. And Nintendo was clearly OK with the Joycons being chunkier as they did release the above as an official Nintendo accessory, people also buy Joycon grips anyway.