I really like my TI-83 graphing calculator but I am not a fan of the fact it uses batteries so I modified it to run on a rechargeable power source instead of standard batteries. The project utilizes a 3.7V lithium polymer battery which is the standard voltage for single-cell lithium cells. I paired this with an MT3608 DC-DC adjustable boost module and a lithium-ion battery charger module to manage the power flow.
The wiring sequence involved soldering the battery to the charger module and then connecting the charger module to the boost module. I adjusted the boost module to 6V to match the requirements of the calculator before soldering it to the power terminals. This step is critical because the boost converter takes the varying battery voltage and steps it up to the stable level the calculator needs to function.
I used Gorilla Tape double-sided tape to secure the PCBs and the battery to the rear housing of the battery cover. Now my calculator no longer needs batteries because I can just plug in a USB cable and let it charge.
Granted with the exposed wires and taped-on components it currently looks like something that would cause a security incident at an airport but it effectively solves a forty-year-old hardware limitation. The next phase of the project will involve a 3D printed enclosure to hide the wires.