Parts (AliExpress)

• Metal Strip 50mm x 8mm x 0.1mm €2.50 (5Meters)
• Pogo Pin (H009 or GB30, 3 Amp), about €1.50 each...
• Pogo Pin (GF55, 8 Amp) about €2.10 each...
• TP4056 (€1 for 10)...
• Magnets (N52 6x3) €4.45 (for 30), or €2.19 (for 10)...
• Length of solid wire (22SWG, about 20cm) ...

I would recommend the larger pogo-pin as it's easier to solder and handle (even if 8 amps is over kill, it makes life much easier).

Note, most 18650 cells I use are charged at recommended 1 Amp, my high capacity cells are charge at 2 Amps. To ensure longer life and greater charge cycles, charge at the lower current (1 or 2 Amp) even if battery can handle more... 

The GF55 Pogo Pin I use is rated at 8 Amps, I use it at 2 Amps for my high capacity batteries... The H009 and GB30 Pogo Pins can handle up to 3 Amps...

We use eight 6x3mm neodymium magnets and a piece of hookup wire (~1mm Ø) to make ground connection and a Pogo Pin, piece of metal strip for the positive terminal with an optional 6x3 magnet for better contact...

To ensure proper contact without a spring mechanism can be difficult (intermittent at best), so we use strong magnets overcome the lack of compression (tested many times, works well)...

One of my batteries is a little shorter (2mm) that all the others, here I had to add a weight to the top of the rotor to ensure contact, all standard 1650's charge without issues. I designed a second rotor to allow for small variations in size (up to 3mm), no weight required, if you have any contact problems, try the new rotor (V9RotorNew.3mf), only takes a few minutes to print...

See Thingiverse link fr more details