When I drive a night with the lighys on, my dash lights will sometimes flicker and the red battery light will glow. Have had both battery and alternator checked and both read OK. Cables are all tight and no corrosion. What else could it be?
Sounds like a bad connection somewhere, loose or corroded, maybe a ground issue. Get a second opinion on the alternator. The “battery light” is a voltmeter that lights up when not enough volts are detected coming from your alternator. The flickering lights and the battery light may not be related to each other.