I have a 1999 4x4 dually Cummings diesel with 2 optima red top batteries which are about 3 years old. Everything will work o.k. for a month or so and then what seems to be out of the blue, the batteries are to dead to start the truck. I think that it has happened more when the weather is cold. Last night, after sitting for a few hours, it struggled to start and then while driving home the headlights flickered every few seconds. And then this morning, after a 35 degree night, there was not enough juice(?) to start it.And then it took a little while to jump start it. I can build you a house but not your engine. Any ideas? Thank you ahead of time.