Recently the car has intermittently stopped.

Recently the car has intermittently stopped starting. Also, when it runs the power will fade. The power fading had occurred in the past about 8 months ago and I replaced the battery (cell tested bad) as well as having the alternator tested (tested good). This seemed to resolve the problem. However the power fading returned when the intermittent start problem started. The symptoms I have with the starting are unusual, when the vehicle doesn’t start I hear nothing, not cranking - started -. - If I come back to the vehicle (anytime later) the vehicle will start right up. Sometimes it will take hours before it starts and other times it could start in minutes. This occurs if the engine is hot or cold. Any advise on where to “start” would be greatly appreciated. Thanks