So i had to connect the battery pack, the charger and the 12VtoUSB converter. I found a left over junction box and got myself some PCB connectors to join the incoming cables fromthe solar panel, the solar charger and the battery packSome leftover plywood (in fact it is special water resistant plywood) was put together with some screws to hold the components - i'm still missing a housing as unluckily in the greenhouse we have quite high humidity and potentially (even though the roof should be water tight) some spill water might hit the devices. So still an area for improvement here...

Anyhow the setup did work (the charger indeed indicated via LED that it was charging the accu pack) and the USB did work. Most important was the voltage measuring device to make sure that Plus / Minus was all connected correctly (as indicated on the battery and charging device). The connectors for the batter i made up from some car supply connectors i still had left over. Even though a crimp device would be necessary to correctly connect i used s standard pliers to crimp the connectors (it works well so far as)