sfromis My experience is that the battery pack can be swapped, if you fold the bike and turn the key under the battery an extra step while pushing it.

sfromis Full charging capacity needs more than the power level provided by many USB ports, often somewhere from 500-1500 mA, if at all. I'd expect it to still charge at lower speed, but charging 4 batteries from 500 mA can be really, really slow.

sfromis Very unlikely, that would be atrocious security.

sfromis No pass through.

sfromis You should not expect it to work, as the specifications says 220-240V. Anyway, I would not expect the lower voltage to be found in outlets with around 230V, which the prongs match. 110V outlets are physically different.

sfromis Using the solder jumpers near the same edge as the INT pin, you should be able to choose between I2C addresses 0x29, 0x39, or 0x49 by bridging the center pad to either L or H.

sfromis You'll have to buy a battery separately, and solder wires from the circuit board to both solar panel, battery and LED module, all with the appropriate polarity.