Only on the 83+. For the 83+SE, 84+, and 84+SE, they are based on the crystal timers, which function correctly regardless of battery level. On all of them, though, the processor slows down somewhat IIRC.

I don't know how much the processor slows down, though... That'd be interesting to know
It shouldn't be significant, though. Probably only 1 or 2 hertz off, anyway (108 times per second instead of 110)

I'm not sure, actually. I know it's around 110Hz, but I dunno exactly.

Only on the 83+. For the 83+SE, 84+, and 84+SE, they are based on the crystal timers, which function correctly regardless of battery level. On all of them, though, the processor slows down somewhat IIRC.

The 83+SE has a crystal timer too? I wonder why didn't TI add a clock to that