Jump start the unit with the old battery in and then take a voltage reading at the battery. At half throttle it should read over 13.5V. If it does you know the charging system is working. If the charging system is good I would take a voltage reading of the battery after I finish cutting. It should be between 12.2-12.8V. If it is park the machine and make sure everything is off. A day later take another reading. It should be very close to the previous day. If it is not you have one of two problems. Bad battery or a bad switch which is allowing a current draw. To check the battery have the dealer do a load test on the battery. If the battery is not covered under your warranty any mechanic should be able to do the test for you. If the battery tests good under a load test, you should have your dealer do the electrical problem search, because as you say it is under warranty. Good Luck, this may take time, as all electrical problems usually do.