I was just going to make a post about this.
I believe they are charging wireless like the cellphones and smart watches.
Couldnt find any pin on anything so that the only thing it could be.
Also heard that the joy-con will charge them self while connect to the switch even if the switch is off. Pulling power from the built in battery.
Seems pretty cool and the controller are said to have a very high battery life so all that should be good.
I do wonder when they will be releasing custom controllers. I can see some kirby, zelda, and mario theme ones coming out.
Also pdp has made a grip for the joy-con (looks like the wii u gamepad)
http://www.bestbuy.com/site/pdp-arm...switch-joy-con-2-pack/5721100.p?skuId=5721100