I had the Mavic Zapp gruppo, which predated the Mektronics...it was not wireless.
Shifting was so smooth and precise, and instantaneous, it was a joy. As far as batteries, all the batteries were required to do was to trip a selenoid valve. The front deurailler was manual.
One drawback was that connection from the wire to the deurailler would unplug easily when pulling the bike in or out of the car. One duathlon I didn't notice it until I got on the bike and had to stop and dismount to find out why I wasn't shifting and lost probably 45 seconds, and it knocked me out of the top ten overall.
Another duathlon it simply failed on me during a race and I was stuck in the middle of the rear cog so I had to finish the race with two gears. So it probably deserved to die a failed project, but man was it awesome 99.99% of the time.
Oh, it was fragile. I had a collision with a car and it was broken in pieces...the external cover was plastic and it could not withstand a crash on pavement. Mind you, My TT bike was pretzled and I was hauled away in an ambulance...it was a bad wreck, but I had the impression a traditional duerailler would have been salvageable.