Quick panic attack

[Lazarus]

Working on getting my vac lines in order got the defrost and vent working. Car was at idle for about 25 minutes. Now it won't start. I shut it off. Now just clicks battery is at 12 v. Put my booster pack on cranks right over. Puff of smoke out of the pvc on the valve cover. Wtf! Never did this before

 

[Lazarus]

Weird either 1 it over heated no steam no nothing.

2. Vapor locked.....its cold outside at idle.

3. My alternator is not charging right.

Weird had it on charge 20 mins fired right up

 

[79 USA 1]

Sounds like a dead cell in the battery.
If the battery has removable caps check the acid level in each cell, if you have access to a battery hydrometer run a check of the cells.If the battery is over 4 years old it could be on borrowed time anyway.