Serial charging 2*2S adapter case

The adapter was designed as a compact expander for serial charging of two 2S batteries.

IMPORTANT: You must to connect batteries of the same capacity and the same model, to charging, with approximately the same charge.

To assemble the adapter, you need 2 pairs (male-female) of XH2.54 3P connectors, 2pcs XT30 male connectors, 1 XT60 female connector, 1pcs XH2.54 5P female connector, 6pcs M2*10 self-tapping screws, a flexible rubber shank, pieces of a breadboard with dimensions like on photo, wires, and heat shrink. It will be safer to fill the inside of the case with glue.
If this option is selected, then before gluing and assembling the case, it is recommended to check the operability of the circuit: first test with a multimeter, then connect the batteries to the charger in the working position.

The holes in the breadboard for the XT30 connector should be made with the expectation that the outer legs of the connector will need to be soldered to the metal pads of the board, but if t