Summary

Prints in 2 parts, the dock has a hole where you can fit an original magnet charger connector that you bought somewhere (On amazon for around 9 Euros).

Or you can print the connector part and solder a 0.75mm copper wire to a stripped USB cable (look at the last photo). It prints as a seperate part because the wire-holes tend to close up due to the plastic shrinking or sagging, so you'll have to drill the holes to get the wire through.

Instructions

Using a magnet charger connector bought somewhere:

Vitamins/Tools

Magnet charger connector
Knife

How to

Print the dock part
Cut the hole at the back to an U-shape so you can lay the charger cable through
Hot-Glue the connector in place and put the cable in the U-shaped channel to lead it to the back and then out through the cut hole.

Using the supplied "connector" part

Vitamins/Tools

Salvaged USB Cable (or just 2 pole cable and USB connector)
0.75mm to 1mm copper wire (about 50 to 70mm)
Isolating tape or shrink tubing to isolate the wires against each other
Optionally: Some kind of magnet that fits the 10x1.5mm slot
Sanding paper
Soldering iron
Wire stripper/cutter

How to

Print both parts (or use the build plate STL)
Drill/Clean the holes:
- The big holes from the bottom are 2.5mm
- The angled holes on the top are 0.75-1mm (you have to get the copper wire through without much wiggling space)
Get some 0.75-1mm copper wire and solder it to a salvaged USB-Cable (Red is +, Black is -, isolate the other colored wires, those are for data)
Put the wires through the holes that they stand out about half a milimeter (+ is on the top of the phone, - on the bottom, do NOT reverse the poles, your phone may be damaged!) and sand them even to make the best possible contact.
Optionally get some small magnets to put in the slot, it helps centering the phone automatically. (I used two 5 x 1.5mm neodymium disc magnets and glued them in)

Sony Xperia Z1 (C9603) charging dock