Was not sure what forum to post this in. Notice that many good bikes have the electronic shifting?

How reliable is this system now?

With electronic would this guarantee 100% accurate shifting all the time. no more readjusting due to stretch cables?

Now do the shifters and derailleurs have batteries in them for this.?

how long do the batteries last? as i am thinking with the Mt bike if u have electronic shifting, the batteries would die quite fast if one is trail riding all the time.