Tiny Sony NP-FZ100 battery charger USB-C

A super small quick battery charger for Sony alpha cameras. Ideal for travel, smaller than anything you can buy (and cheaper as well). Unlike my camera (Sony A7IV) which is very picky about the AC adapters it accepts for charging, this one works with basically any AC adapter. This project got started after I made the mistake of not taking along the original Sony charger on a vacation trip...

The NP-FZ100 consists of 2 Li-ion cells internally (7.2V), so this requires a so-called "2S" (2 cells serial) charging circuit with 8.4V charging voltage. The one used here is available in online shops under keywords like IP2326 2S lithium battery charging module 8.4V USB, it supports QC 3.0.

Safety advice, pay attention:
Li-ion cells are dangerous if mistreated. The charging circuit used here can be bought in 2S (8.4V) and 3S (12.6V) configurations - make sure you buy the 2S one or your battery will go up in flames!! Similarly, make sure to connect the battery with the correct polarity! I didn't try it out (and you should not either), but in the best case a wrong polarity will fry the charging circuit, in the worst case (if the NP-FZ100 has no protection circuit which is unlikely) ...your battery will go up in flames. See the picture for the correct orientation and connections between the charger and the connector. Also beware to connect the correct 2 battery contacts, the middle of the 3 remains unconnected. Finally, use somewhat thick cables to connect the charging circuit, as the charging current is quite high.

More info on the charger:
This is sold as a "fast charger". The IP2326 IC allows selecting the charging current via an external SMD resistor (which you can re-solder with enough skills), but by default I think it comes configured for the max supported charging current of 1.5A. This is fine for the NP-FZ100 - since it is rated as 2280mAh it gets charged at 0.66 C, within the recommended range of 0.5 to 1.0 C.
The module will restart charging once voltage drops <8V - so I would recommend not to leave a battery connected to the charger (and USB-C power) permanently as the repeated re-charging is not optimal for battery lifetime.
See the IP2326 datasheet for full information about the chip.

Building the battery connector:
The most challenging part of this device may be the mechanical connection to the battery. The metal bits that slot into the battery need to be the right thickness - too thick and they may damage the battery contacts. I salvaged some pieces of solder-able metal from the battery compartment of some battery-operated device. It helped to slightly "sharpen" the edges where they need to slot into the battery by filing them. Also, the distance between the contacts needs to be exactly right, this is not too hard if you align with the battery and clamp the metal bits in place before soldering.

As can be seen from the STL files, the idea is to screw the two pieces together and fix the small PCB with the connector in the process. But just glueing everything together also ought to work.

Printing:
See the picture for a recommended configuration to print. The 45° tilt gives a nice texture on all sides, but needs a brim and possibly some small supports to print correctly.

PS: This is the second iteration of this device. At first I tried to use an IP2369 board which would have turned this into a small "emergency powerbank" for your phone, i.e. the board supports both charging and discharging. Sadly, this didn't work out. The chip always decides to promise too much current to the phone, which this little battery cannot deliver.