Finally found it (and created Readme.md + GH Repo)

My long, arduous search for a 3.7V Li-po/Li-ion battery has finally come to an end.

Since my local area has quite strict import of dangerous Lipo battery rules, I had to go find a LiPo battery from local vendors. This actually took way longer than I expected, because I refused to believe that the Mouser Electronics and DigiKey websites were legit. Turns out, they literally have a headquarters here in Hong Kong. I can source my battery holders from them

The problem was always this - the battery was too big and bulky. A flat rectangular LiPo battery would fit into that box nicely, but it wasted a lot of space for the flat solar panel, and the space I had constrained the volume I could put. So I decided on 3.7V Li-ion batteries - the little cylindrical ones.

Here’s a cool thing I learnt. Many electronics projects use the 18650 battery, but I never knew what it meant until I found its AA(14400) and AAA(10440) counterparts. It is actually very systematic:

• 18(mm) is the diameter of the cell
• 65.0(mm) is the length of the cell

Isn’t that cool? Just wanted to share that.

So finally, I decided to use the 10440 batteries (3.7V, 350mAh), and I would also need keystone clips to handle the 2A+ current draw from the RPis. I can insert these clips into my 3D-printed case to save some space.

Things I need to do next:

• CAD case: hopefully this is less cortisol-demanding
• Firmware and software
• Finish Readme and submit this project for funding

I’ll see you soon, probably taking a break over the weekend due to some family visits.