Q: Car left two days didn't start third day, lights go on, no start up. AAA battery charger started car.

Hello. It sounds like you have a battery issue. If the jump starting got the vehicle going then that means that the battery alone could not produce enough power to start the vehicle. If the battery is low enough it can power some of the lights and other electrical circuits in the vehicle and just not crank it. If you want to have your battery checked, consider YourMechanic, as a certified mechanic can come to you to [diagnose why the car does not start] https://www.yourmechanic.com/services/car-is-not-starting-inspection

Hi. This problem sounds like the battery is bad and needs to be replaced. Once the car is started the charging system can be tested to see if it is charging the battery like it should be. Replacement of the battery should be first then testing of the charging system should be done so we know that the alternator is not killing the battery from not charging. We have certified techs at yourmechanic that can help you with changing your battery and testing the charging system.

This is a sign of a weak battery. When a battery is too weak to turn the car’s engine over, it may still have plenty of strength to power the accessories such as the radio, lights, fans, etc. In your case, it sounds like the battery needed the extra power provided by the battery charger. As you may know, most battery chargers have a separate mode called a "boost mode" which provides enough power to get the engine started so that the alternator can then take over charging the battery. I would recommend having a professional from YourMechanic come to your location to replace your battery.