new to elec, wondering about the batteries, the blade cx comes with 7.4v 800mah 2cell batts. Can you use 7.4v 2cell batts with a higher mah rating. will it hurt anything, or just give you longer run time?

As long as you only use a 7.4v bat, you can use a higher Mah rating. The problem you will run into is placing the larger size packs into the battery harness. Longer times means harder wear to the engines, so let those motors cool between flights. I was told to fly for a few minutes, then let it rest for a few for peak motor performance.