About the charger and the lights: I may have overlooked the model number of the Kobalt, and I do not know your battery chemistry. As previously stated chargers usually were sold with the end item and were specific to battery type. Lithium batteries have internal BMS electronics to make sure you don't over charge more than 90 % of usable power. This is because the charger senses the open terminal, no load of the suspect batteries and adusts internals to match charge parameters so it will not over charge. During charge cycle, the charger monitors temperature, voltage and current so that when the lights indicate a READY for service you can rest assured the battery has been recharged to close to 100% of capacity. Nicad, NIMH, LeadAcid and other variations of lead acid use a different type of charger. You need to be certain the charger is specific to your type batteries and that the charger is functional. The manual fpr the mower, the manual for the charger will tell you how to safely charge.
One word of caution. Lithium batts output full demand current for cutting grass and suddenly the BMS will shut down the battery because it is at <10% charge. Do Not repeatedly hit RUN; BMS has to draw a little power to re run the sense voltage again to determine battery status. This pulls the 10% down even more and if you continue it will not have enough no load load voltage for the charger to act on and will status the battery as a hard fail. The lights will give you an indication of battery condition. Some one else mentioned the soft start. When you pull the trigger the motor is almost a short circuit and as such demands an extremely hight amount of current except for the BMS monitoring the discharge rate and will limit that current until it is within the RUN spec for load. The Battery Management System is a small computerized integrated circuit wired internally in the battery. It is a great system and works well
with a little care and maintenance. As a aside; you could have a one battery, two battery or a four battery configuration. I am thinking you have the simplest of a single 12 volt battery running a single speed motor turning a single SHARP blade and a putting green quality lawn to maintain. OR YOU COULD HAVE an extension cort that converts 120AC to a DC to run the motor. A model number put into this site will get you on the right track. This is a simple problem and no one has mentioned if you plug it in to the AC wall plug or run it off self contained batteries. Dude, the dang thang is broke. OR you could get POE to help you with the troubleshooting.