The TI-84+/C/SE uses a linear voltage regulator to drop the voltage coming out the batteries down to 3.3 V. Then, inside the ASIC, it uses a charge pump to boost the voltage back up to 5.0 V. That charge pump is not active most of the time. You'll need an assembly program to turn it on. It would be unwise (though probably harmless) to attempt to connect the calculator to a computer when the charge pump is active.

Do not attempt to wire the USB port directly to the batteries. Doing so could damage anything you connect to the USB port. If you're willing to disassemble the calculator, it would be better to cut a hole in the calculator to make your own port for the light. Though, by then, you might as well just make it a traditional backlight controlled by a switch.

If you really want a backlight that much, you could also buy a TI-84+CSE. . . .

If you really want a backlight that much, you could also buy a TI-84+CSE. . . .

It probably depends if he wants to deal with slower speed, though (although it's only really bad if he types stuff but need to modify it or for editing large programs, but otherwise it's not that bad). The problem with a 83+/84+ backlight is if not done properly, then it won't look pretty. The Casio FX-9860GII calcs, which use an LCD similar to older models, but have a backlight, do a pretty good job. However, from hardware modders, I did see some horrible 83/86 backlights before, like at , but I saw some that are kinda good, like

Welcome here by the way GuyRobo!   We also have an hardware modding/technology section on the forums, but it's located outside the calculator sub-forums since it's not specific to calculator modding, unlike here http://www.omnimaga.org/index.php?board=145.0