I have heard that all the maxtrax is is a timer and impact sensor. There is a little switch/butto on the side that is held down on the side of the body tube, and at ejection, it releases the button and the timer starts counting. At impact, it tallys the number of seconds and gives you a readout. The trick is to fly it on a very short grass/no grass field so it wil detect impact.
The Max Traxx is not an altimeter. Just a timer that starts upon ejection and stops on impact with the ground. The assumption is that it falls at a pre-determined rate of decent and you can calculate the altitude from the time given by the device.
that is very normal. remember, make sure to fly it at the desert, or on a low/no grass field. Sometimes though, it just doesn't arm itself right. I would say, just as a guess, replace the small battery after every three or so flights.