Does the negative cable spark a lot when removed and replaced?

To drain a battery overnight it takes quite a bit of amperage. Unless the new battery has a bad cell. Internal shorting.

I usually connect an inexpensive meter between the ground and the body of the car. Harbor Freight sell them for about 4 bucks. They go up to about 10 amps. They are digital and will display any draw less than 1 amp.

If you find a draw you go around and look for what may be on or do the fuse panel elimination method mentioned on the other post.

If the car draws more than .1 to .2 amp. resting. With all things off. You got more than a drain of a clock, alarms, LED's or computers.

It should then spark in daylight if it's a heavy draw. It may have to be dark to see a .5 amp or less. If you hook a 12v light bulb between the negative cable and the body then there is a circuit to cause a drain proportional to its brightness. Just in case you don't have a meter.

Phil