2001 Ford POWER STROKE
 

TRUCK WOULD SET FOR TWO OR THREE WEEKS BATTERY WOULD GO DOWN. HAD THEM CHECKED THEIR GOOD. THEN I WOULD HAVE TO PUT BATTERY CHARGER ON IT TO GET IT TO START. EVEN THO IT TURNED OVER GOOD. THEN I WOULD HAVE TO PUT CHARGER ON IT PLUS PLUG IN THE HEATER TO THE ENGINE SO IT WOULD START. IN ALL CASES ONCE THE TRUCH STARTED IT WOULD START FINE THE REST OF THE DAY ON ITS OWN WITH PLENTY OF POWER AND NO TROUBLES. I HAVE ALWAYS WAITED FOR THE START LIGHT TO GO OFF TO START THE ENGINE SINCE IT WAS NEW. MY THINKING IT MIGHT HAVE SOMETHING TO DO WITH THE GLOW PLUGS BUT I COULD BE WRONG. THE TRUCK HAS 64,540 MILES ON IT. DO YOU HAVE ANY IDEAS?

Sounds like you should load test the batteries. If you leave it sit that long then run it a little they aren't getting enough time to fully charge. A trickle charger or battery maintainer will help you.