430 How is my battery dead if it sits on a battery tender?

Driver's door not closed properly and internal lights came on?

The same microswitch on the latch/lock mechanism in the door does the following:

Controls the interior lights
Drops the window
Turns on the F1 pump (assuming the battery isn't flat)
Turns on the door open light on the dash (if the key is on).
Tells your Alarm ECU that the door is open.

Try locking the doors with the fob. If the door is not closed properly or there is something wrong with the microswitch, the locking may be rejected. Does your siren beep more times than normal with one of the doors open?

I'm not sure if they use enough power. There is a blue wire on the OBD2 port which supplies power from one of the car's fuses to the diagnostic tool.

 

Could it be the tender was not plugged in or broke
Yes the dongle will drain it but not if you had a working tender connected
Check that the tender is actually working

 

Do you have an actual Battery Tender or a battery maintainer?
The standard Battery Tender is 1.5 amps.
The Battery Tender Junior is 750 milliamps.
If you had a draw that was greater than the output, it would eventually discharge your battery.
If you have a battery maintainer from another brand, you would have to look at it to check the output value.

It's also possible your battery is bad even though it's only 2 years old.
@flash32 also made a good point about it not being plugged in. Whenever I hook up one of my Battery Tenders, I always look at the light on it to ensure it's hooked up and charging/maintaining.

 

I had a tender go bad on me before. Is Granite Digital still good? I see they are on Amazon now.

 

https://www.batterysaver.com/store/p78/2365-lcd.html

A winner, IMHO.