As for the range of the battery, I'm guessing since you are in Texas perhaps you spend alot of time on the highways or on secondary roads without much traffic and perhaps are going quite fast with the battery, maybe upwards of 55 mph?
In order to get alot of miles from the battery, you need to try to close all the coach bars to full blue. This means gentle acceleration no more than 2 bars on the Empower screen (out of 4 bars total with a charged HVB), braking at a slow and steady pace and anticipating all the stops way beforehand so you don't actually use the brake pads much at all and regenerate back into the battery to further increase your range.
Finally speed needs to be at 40mph max on the battery or less. Ideally 20 to 40mph in the daytime works good. At night 35 to 40 mph is better as speed is of the essence the car's lights are burning the battery all the time and you need to get there sooner than later, so try to drive in the upper portion of the range if possible.
If you hit an open stretch of road and need to go faster than 45mph, ideally start the engine and burn some gas. Don't stress out the battery by driving fast with it and continuously (that's what driving fast does) put a high load on it. The slower you go the less the load at constant speed. Of course there is a higher load during acceleration, but that's momentary until you get up the speed and then the load drops.
Get the coach bars to full blue and your car's range should go up significantly.
Stepping back for a minute from that, you're in Texas (a hot place) and you've got a 2013 Cmax so its 5 + years old in the heat, so chances are you've probably had alot of opportunities to damage the battery from overheating unfortunately, so it may not at this time produce as many miles as it could when it was new. You situation may be different if you just recently bought the car and say perhaps it came from a cooler climate like New England for example. In any case you need to try to not overheat the battery if you're concerned about range.
On the 2nd thought in my head, if you say the hybrid battery drops pretty quick when the AC is on (that adds about 2 amps load when the car is cooled down to the battery, probably more in Texas where its much hotter), then it may be an indication that some of the cells in the battery are puffed up and can't take the load well at the end of the charge hence why the battery crashes much faster than expected.
In any case do NOT use the entire charge first and then go to hybrid mode. The only reason to do that is that if you know for sure you will get to your destination on 100% EV, otherwise if its not possible then use the battery piecemeal where it works best and start the engine for the other parts of the trip. This way you don't heat up the battery quickly by draining it in the first 10 minutes it should last you at least 1 hour of your trip if not more.
Hope this helps.