It's alarming how naive some people are about battery technology…
The 3 hour max is only for dev kits, Nintendo will increase it to 5-6 hours for the final retail product.
Uhhh, how? Will they wave a magic wand and say the magic words?
There's no way to include a battery into the Switch's tablet-sized form factor large enough to provide any more than about 3 hours worth of the processing required for full console games. Besides that main bulk power requirement, there's also the screen to deal with, as well as background apps and potential Wi-Fi connections.