Hi. My 56v battery has been failing frequently in the last few months. It stops working in the mower and rapidly flashes yellow. Usually, I can then put it in the trimmer and it works again. But now flashes in the trimmer too. If I press the battery button, it also flashes yellow. In the charger, the charging light flashes green, while the battery light cycles through red, yellow and green. Anyone know what is wrong?