Why won't my Hyundai Santa Fe start in the mornings?

About a month ago, in the morning, I got in
my car and everything turned on fine and it
cranked but would not turn over. After a few
tries and car continuing to crank it finally
started up. This happened again the next  2
mornings. I bought and changed out a new
battery and did not have the problem again
for about a week and a half. Then the same
thing but only in the morning. Once the car
is started up I do not have a problem for the
rest of the day other than it occasionally
stalls an idol or reverse. I have taken it 2
mechanics and they both said everything
checks out fine. Battery, transmission,
starter are all fine.  I have also never had
any indicator lights on my dash to go off of.
Thinking it's possibly a battery drain I kept it
on a charger overnight and it started up
fine. After being on the charger it started up
fine for 4 days other than stalling twice.
Now this morning on the fifth day it took
three tries before it turned over. Please
someone help! I don't know what to have
checked next. Is it electrical? Is it the fuel
intake system? Is it a bad crank shift
sensor???