Has it ever done this while the dealer had it for repair? If you repeat the problem there is a check I would do if I were working on it while it not powered up. Remove the back battery cover to access the ground (-) terminal and cable end. with car exhibiting the no electrical power check from batte...

If the internal connection goes open that means the connection is broken and there would be no voltage measured at battery terminals. WHen that happens the connection can cool off and then battery has power at terminals again.