I hardly drive my truck, but sometimes when i go to drive it, it wont have enough juice to start immediately. It will crank for a sec or 2 then just slowly stop. Then I charge the battery with a charger, and its good to go. I have a dummy alternator light. At idle it doesnt start charging until i rev it up a little, then the light goes out. Any idea what could be causing this? Ita a new 100 amp alt model number is dl7157 from autozone with a lifetime warranty. Its also a pretty new yellow top, so i really dont think its the battery.