Hi, I have Ego 21" self propelled mower with the 7.5ah battery. After a few using it a few times, I noticed the self propel function will stop after about 10 feet. If I release the lever and re-engage it, it will work for about another 10 feet....! The blade continues to turn, but no power to the wheels. It happens on all speed settings (I get a bit further at a faster setting). I have tried using a different battery with the same result. Could there be a short somewhere? My warranty is almost up!