Battery drains over night with check engine light

It all started with my old battery being drained. Charged it up to see if it would turn over. It did not so I got a new battery. Put it in. And it started just fine. As I was walking away I noticed the check engine light on. With the keys to the truck in my pocket. With it being late decided to look at it the next day. Next day rolls around an battery is completely drained. Charged that one up. Tried to pull codes up but nothing would appear. After a few times of letting it run. Turning it off. The light would go off. And everything seemed normal. Took car in the a shop to see if they could see anything. Of course the light did not come on for them. And they could not find any problems. So took it home parked it. Next day, getting ready for work went outside to start truck up. Looked on the dash. Light was on. Tried to start it. And it was drained.