Here's what happened to me:
I bought an extra Wiimote and Nunchuck, that makes 2 Wiimotes and 2 nunchucks.
First, I was just playing baseball, and then, the 2 Wiimotes dead, the led lights at the bottom of each one where dead, and I tried to sync them again, but it didn't work out, just like 5 minutes later, the Wii (Not the controllers), made a really weird sound, and just then, the light of both Wiimotes were on again, and everything was working fine. The next day it happened again, exactly as before.
Now I just wanna know what could this be and if somebody has experimented something like that.