Nokia N900 Necromancy – giving a new life to a classic Linux smartphone

Summary

Nokia N900 Necromancy Building a fake battery, adding a USB-C port, booting from SD card, and giving a new life to a classic Linux smartphone. My friend Dima sent me his old-school classic Nokia N900. The battery is very old, and it does not boot as-is. So naturally, I wanted to see if I can resurrect it. Step 0: Is such a thing even possible? Yes it is! (Unless there are other hardware issues) I ran a smartphone without a battery a few years ago. Cut and soldered a quick prototype to connect instead of the battery. Resistors are to emulate the "normal" temperature by providing expected resistance between the third pin and ground. See link above for details. Hooked up a large supercapacitor to the battery pins and to a +5V source. If I recall correctly, using a capacitor without additional power did not work. And it boots! Now, let's make something that can fit into the battery compartment. Step 1: Better "battery" These supercapacitors are nice, but way too large. After searching on Mouser, I found FM0H473ZF, 47000 mF (0.047F) capacitors in a rectangular case that is only 5mm thick. Ten of these (~0.5F) is enough to run the smartphone without dying. Capacitor contraption (TM) arranged (using a 3D-printed template) and soldered together. And they all fit nicely into the battery compartment. The power is provided by a wire routed through the hole for the carry loop. Running fine! One noticeable issue is that capacitors are getting pretty warm. Probably my sloppy soldering, but no shorts that I could find. ⚠️ This is where I should have stopped. At some point while messing with the "battery" and power, I managed to corrupt the internal partition and the installed OS. Not sure if this was from the sudden battery pull or from supplying +5V instead of the expected +4.2V to the battery pins. Luckily, newer Maemo Leste is intended to run from the SD card anyway, and internal storage still works, so I was able to overwrite it with the bootloader. Bootloader setup on Maemo W...