Lights flicker Always

Had the battery changed. They say not the alternator.
The lights brighten and dim inside And outside the cab. If I am behind a car at night I can tell that they see the lights going off and on.
When I try to use an inverter in the cigarette lighter it has the same problem.
Power surges are more like a flicker now than last year they were less quick.
Yes this is an on going irritation.
Can you figure it out?
Thank you,
Lori