I don't have any specific knowledge of your car in particular; rather this advice is all applicable to most any car with the same kind of problem you're having.
So you get up in the morning and the car won't or has trouble starting due to the battery being low is what I'm hearing; correct me if I'm wrong. If that's the case, then you've got three main things to check to figure out what's going on with your car.
- The Battery. As batteries age, they lose the ability to hold a charge. Eventually it gets to the point where it can't be charged enough to start the car. If you're located in the U.S., most auto parts stores will test your battery for free. They may be able to do a simple test with the battery still in the car, or a more extensive test if you pull the battery from the vehicle and take it in by itself. If you do take it in for testing, charge it first if you can, as the testing needs a charged battery to work. If you can't charge it manually, the auto parts store will have a charger but of course then you'll have to wait for the battery to charge before it can be tested.
- The Alternator. It will generally put out around 14.5V DC when the car is running in order to charge the battery. It's fairly easy to test with a voltmeter; first check the battery voltage with the car turned off; you should be seeing around 12V on the terminals. Start the car and you should see the voltage go up to somewhere around the 14-14.5V area. If it doesn't, then chances are the alternator isn't charging the battery enough to power the starter. Same testing strategy goes for the alternator as the battery; many stores can test it while it's in the car, but others can do much more complete testing if it's out of the car and can be installed in their test machine.
- Otherwise both of those items might be good but your car still isn't starting after sitting overnight. That would tend to indicate that something is draining your battery as it sits in the driveway. Disconnect one terminal of the battery and connect an ammeter between the battery and the terminal so you can see if there's current flowing. There will usually be a very small amount to maintain things like radio settings, etc., but a larger current draw could indicate the problem. Generally pulling fuses is the quickest way to pin down where that current is going; look at any aftermarket products that are installed first.
That should give you a place to start to get your CX-3 fixed. Check out the things I've mentioned and let us know what you find.