They traded away aesthetic for the return of functionality.
How is this objectively bad?
I'm a man who values looks before functionality but even then I have to say that I can approve of this. AA batteries will always be more functional than lithium ion in the event that bulk and weight are of no concern.
Well... like I've pointed out with the new Apple wireless keyboard, aesthetics didn't need to be traded for functionality. At least that's the way I look at it.
How are AA batteries more functional? A Li-Ion will last longer, you don't have it sticking out, and you don't have to replace the batteries. Saves a lot of hassle if you ask me.
li-Ion will eventually die (and if it does so in a poor fashion it could cause a good amount of damage) Rechargeable AA's are cheap simple to replace. When in smaller tech like this i always prefer an easily removable battery source hence as i mentioned earlier loved when Logitech moved the G602 to AA's. Given when the run time on batteries is so long when you can use 2 AA's i don't see the real advantage of a li-ion.
THe Li-Ion if inside the board could end up damaging it should anything bad happen with the battery
An internal L-ion is much harder to replace then two AA's and whom is to know if they would use a proprietary size/battery cable etc
If it happens to die when i am not near a charging source or i don't have time to connect it and let it sit and charge i can swap out AA's easily on a whim or even buy some should i not have rechargables with me.
Short of a major case redesign i'm not sure they could fit a battery big enough inside the case to provide longer lasting power than 2 AA's can? I mean panasonic eneloops are 2550 mAh /AA Do they make safe li-ions small enough that could fit inside the case to compete with that these days?
It's all subjective of course but personally with devices such as this i tend to move toward AA's over rechargeable internal cells.