lights flickering on 2003 Toyota Avalon

what are the possible causes of lights flickering on my vehicle. the interior lights and headlights pulsate when i first start the car and then gradually stops. all electrical components and systems operate fine but the power seats make a clicking sound when functioned. battery is charging and in fair condition. any suggestions?

Asked by for the 2003 Toyota Avalon
The battery has been charged and tested under load (using a high rate discharge tester and battery hydrometer)? Ensure the battery connections are clean secure and tight. Put a volt meter across the battery at rest it should read 12.6 volts, get a friend to start the car, the voltmeter should instantly read approximately 14.6 volts. I suspect the alternator may be failing. Does the battery light come on brightly when the ignition key is turned on and go out immediately when the engine starts.
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A weak battery will cause the flicker. Mine did the same thing until I replaced the battery. That was at the 6+ year mark. Not bad for an original battery.