Eliminate the basic stuff.
Remove the battery cables from the battery and clean them and the battery posts. Reinstall.
When the system is dead do you have voltage at the battery terminals? Test light will do.
Have the battery load tested at Autostore.
Also, sometime the lugs on the battery cables are corroded internally and make an intermittent connection to the wire. Replace the battery cables.
Check if the grounding jumpers are installed, connections must be clean and tight. Grounding jumpers are frame to engine and frame to body.