Car battery keep dying - any idea why?

Battery keeps dying in my 2004 ford card - for the past two daysn even if i keep the lights turned off - and i had to jump start it each time… There's only one time i left the headlights on and battery went down. And it was only for 30 mins. And still doesn't explain how ti could drain so quick. I take my car regularly every day…
only thing i could think of is, i usually keep the gps connected to the 12v port all time even when the car is turned off… Could that be a reason. Or is really time for battery replacement.
is there any place where i could get free battery testing.

Most auto parts stores will test your battery at no charge. There's a good possibility that the battery is failing due to an internal electrical leak that is not a dead short, but is enough that the battery goes down on it's own in a short time.

Other possibility is an alternator (or other electrical component) problem that is drawing the battery down. Part of a battery test is to check the voltage both while connected and when disconnected. That will reveal an external draw - alternator being the most likely.

You can go to advance auto or auto zone or any auto parts store really. They will check battery and alternator for free. And some mechanic will do it for free.

If your battery is original or more than 4 years old, its time to replace it, also check to see that your alt belt is adjusted properly

Easy answer, your battery has gone bad. They don't last forever. Just like cell phones they eventually lose their ability to hold a charge.