Originally Posted by LayWithTheZJ
It's not my battery because I get power to things inside when in on position
This does NOT rule out your battery. The dash gauges, radio, etc. take very little power to work. Starting your engine demands a big power draw from your battery.
And I know your battery measures 12.5 volts. But you should know that voltage testing of a battery is really not conclusive.
You need to have your battery "load tested
". Any parts store will do this for you for free. Load testing is the ONLY accurate way of determining the condition of a battery.
Yes there certainly are other possibilities, but you really haven't ruled the battery in or out quite yet. I'd be sure to do that so you aren't chasing your tail.