Inspiron 13 7000 old battery

My laptop stopped charging then died once the battery ran out.   I got a warning the battery health is bad. I'm waiting on a new battery. The laptop will not turn on with the battery removed and the ac cord plugged in.  The battery is several years old and slightly swollen. 

I measured 19.5v dc out of the cable and the internal charging port. I then measured 3.1v dc at the board connector for the battery with the battery removed. So the laptop is receiving power but won't turn on with the battery removed. 

If I drain the power by removing the cord and holding the power button for 30 seconds, reconnect the cord, then power up,  the laptop will turn on with a low battery warning but only for a few seconds. 

The new battery should arrive in a few days but why won't the laptop turn on with the battery removed and the cord connected? The cord, jack, and board are good. All research says it should turn on.