What would make the instrument panel brake & battery lights come on at the same time and stay on while driving my 2006 Nissan Altima 3.5? Brakes felt OK.
It could very well be your alternator has gone out. Open the hood and put the probes from a multimeter set to vdc onto the battery terminals. Observe the voltage of the battery with the vehicle running. If the voltage is slowly creeping down, your alternator is not functioning (it's not charging the battery, so the engine is absorbing the energy to keep running).