What would make my car loose voltage and not start from one day to the next

Weak battery, lights and gauges still work but the battery is too weak to power the Starter

Yea but I took it to get checked and they said the battery reads full just one voltage short of where it should be. After having it checked as soon as I got home it would start back up .

Maybe a bad positive/negative Terminal Connection thats corroded or not tightened down enough, clean up the connecting area with wire brush. Ground wires connected to engine may be loose. This will cause a one click when starting the car too