The Qt Py now has a BFF, specifically - the Adafruit Charger BFF for Qt Py.

I've attached a 350mAh battery and the negative cable immediately broke... I attached a larger 500mAh battery while I resoldered the cable and designed a new larger case (v4 now) to accommodate the  combined Qt Py and BFF.

It was late in the evening, so of course the screen doesn't fit, I forgot to re-extrude the screw holes and the battery cable is too short (questionable positioning aside)...

The picture above features the larger battery. I've also realised the short-cable version of 350mAh lipo battery is much bigger than the long cable one so I'm investigating alternatives... I've also ordered a smaller OLED screen which should allow making things more compact still, though I lose the Stemma Qt quick prototyping advantage there. On the other hand, the screen and battery are the largest space consumers although the BFF bulks things up too, but if all goes well down the line it can all be put on a single PCB.

Next up - I'm printing v5 of the enclosure though I'm reusing the lid from v4. Since only the BFF has an on/off switch and it'll be hidden, once I have everything in a nice neat package I'll start looking at the putting the Qt Py to sleep... and waking up with interrupts, most likely taking advantage of capacitive touch. And it would be nice to add a battery level/charging indicator as the BFF has a voltage divider connected to pin A2 and I should be able to figure out battery/power state from that.