Spring-less Dual 18650 Holder (w/ Charging Module)

I'm working on a project in which I want to power some Wemos D1 minis using 18650 for a few hours at a time. I bought some battery holders on Amazon but they were terrible - cheaply made and the form was so tight that the spring wouldn't push the battery up to the positive connection. I went ahead and designed these battery holders instead.

The design is simple, there's a top cap with a slot for a charging/protection module and a bottom cap for just the batteries. You use simple tabbing wire (often used in custom solar panels) for the leads. 52mm of 5mm tabbing wire will be used for each end. Fold over the wire at 12mm from each end and insert through the cap, then fold around the detents. Place rubber bands in the notches on the holder top and bottom to pull the tabs onto the battery leads.

The charging/protection module seems pretty common and I've linked to the ones I'm using below. The module should slide into the slot pretty snug. I used hot glue both as an insulator for the (very close) board leads and to hold the board in the lot. There is a long slot running to the bottom of the case for the lead wires and a slot in the top to charge without removing or dismounting. There are two outer shells, one with mounting holes and the other is just plain.

In my tests I was able to power a Wemos D1 mini powering 26 NeoPixels for about six hours before they started to show any sign of power degradation - and even then it was some very light flicker at the end of the string. At around eight hours I stopped the test with not further degradation.

Disclaimer: Obviously when working with LIon batteries you need to be very careful. These things can explode so if you don't know what you're doing maybe pass on this project.

What I used - apart from the printed parts and basic hookup wire:
Charging module: https://www.amazon.com/gp/product/B071RG4YWM/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1
Tabbing wire: https://www.amazon.com/Nickel-0-1x5mm-Battery-Welding-0-15mm/dp/B07W6VFFYS/ref=sr_1_2?keywords=5mm+18650+tab&qid=1584331035&sr=8-2 (I actually used .2mm x 5mm but that seems to be no longer available)
18650 Batteries: Since I'm using my own protection circuit I'm happy with non-protected batteries. There are a lot of fakes and questionable batteries on Amazon so maybe stop by your local 'vape' shop and ask them for a decent battery.

Keep in mind that the module above is a charging module and only delivers battery voltage (~3.7-4.2) out. That fine for the Wemos and for the NeoPixels but if you need a constant 5v or something you'll need a different module.