In 10 minutes I threw together a 3S 2200 mAh pack and started charging. Cells were highly unbalanced and had been restored from the deep sleep state with a constant voltage about one month ago. They measured something like 3.2 and 3.6V unloaded.
The "Mystery B3AC" charger reports a worrying "do not leave charging unattended". It should charge a 3S pack at 1A and 2S pack at 1.5A.
I was listening to 2m SSB when I first plugged the battery pack and a strong QRM appeared. Uh! Oh! The charger is absolutely NOT RF-friendly! (No, I haven't checked if the noise was coming through the antenna or the PSU) I looked every now and then what was happening in the shack, without monitoring the actual DC current flow. The charger temperature was high, it was smelling too. I couldn't almost keep my hand on it.
Nevertheless, about two hours after charging, first LED turned green, shortly followed by other two. Temperature returned normal.
Next step will be to power the FT817 with this 11.1V (nominal) pack while studying the charger circuit.
So far .. no fire.