HP 110 Plus Lithium Battery Pack

Introduction I have this HP-110Plus (HP45711) which uses a very old tech sealed lead-acid (SLA) battery. Those batteries are heavy, hard to find in this specific dimension, and need constant baby-sitting and recharging to be kept alive. Why not bring your favourite laptop (I am sure) to the 21st century and have a lithium battery (that can also catch fire without warning) instead? On top of that, you can now ditch that old 8V AC HP82059B transformer (as it is falling apart anyway) and use USB-C power delivery instead! What's not to like? Design files for this project are available publicly on OnShape. What you need The battery pack is all based on one of those two-cell UPS that you can find for cheap on AliExpress. Only, because 6V output is not offered, we will have to do a little desoldering and soldering to fix that issue. I picked the 9V USB-C version as a base. Then, as the USB connector is not conveniently placed, we'll have to move it around, so I used those plugs. I like those