Due to various first-world problems, my wife and I ended up with two different Panasonic cameras. I use quite interesting LX100 while she strongly prefers FZ300 and zoom it brings.
FZ300 uses lithium-ion DMW-BLC12 battery (7.2 V, 1200 mAh, 36.0 x 48.0 x 16.8 mm) and comes with DE-A79 battery charger. My LX100 is a bit smaller and uses DMW-BLG10 battery (7.2 V, 1025 mAh, 37.0 x 42.0 x 14.1 mm) coming with a smaller DE-A99 charger. As you can see from measurement, it is not the same battery. And no, neither charger is designed to be universal.
However, pinout and voltage is the same on both and you can sort of get smaller LX100 battery into FZ300 charger. Unfortunately, as battery is shorter, it doesn't stay in nor it charges. Only if I could find common house-hold item that could bridge that 6 millimeter gap in length...
Well, it ends up that 4.5 mm of USB connector is just enough for flexible pins on charger to make contact with battery. And my old SanDisk USB drive fits just right.