I got round to building an iSpindle last weekend (after having parts dribble in for what seemed like forever). I have gone the wireless charging route too, and am using the following product:
https://www.aliexpress.com/item/Wireless-Charger-Receiver-Module/32279028531.html
It gets a little warmer than I would like and doesn't have two way communication smarts to turn itself off (like the cell phone ones do) but charges the battery successfully. I just turn it off when the battery lipo charger board lights up blue.
The receiver coil fits inside the inner lip of the lid of the PET bottle so the bottle can sit upside-down on its lid and charge.
I aim to never open my bottle once it is calibrated so I picked up a couple of magnetic reed switches (
https://www.jaycar.com.au/glass-reed-switch-n-o/p/SM1002) from Jaycar.
One to replace the toy switch (to turn off the device when sitting in my charging station), and one to replace the Wemos reset switch so i can double tap the switch to enter config mode.