E-Blox® - Power Blox™ Battery Block

The no-wires part is what sold me, and it actually works. My daughter built a little light-up house and the battery block clicks right into the base so nothing comes loose when she carries it around.

My son figured out how to snap this battery block right into his brick creations and the LEDs lit up on the first try, no wires to fiddle with at all. It takes a standard 9V so I just grabbed one from the junk drawer.

Does the job once the blocks click in, but the connection feels a little loose on one side. My kid still gets the LED to light up, though I have to press it back down every so often. Fine for the price, just not as solid as I hoped.