Car won't start. No lights no crank. Nothing

So the battery being good rules out the alternator being the problem? No lights rules out ignition switch? Wrong on both counts. First off the battery needs to be charged and tested. Secondly the battery cable and ground cable connections need to be absolutely clean, free from corrosion and tight and this includes the connection to the starter and the short cable that goes from the positive battery cable to the under hood fuse box. Also check the battery ground connection at the engine as it also need to be clean and tight. Once you have good battery voltage and clean connections then see if it will start. Was the check engine light on?

low voltage is the issue. if the battery is 4 years old or older you should replace it.even though you had it tested does not mean its good.