When the car seems dead, will the headlights for example work?

 

No power, lights, nothing. It's exactly like a dead battery.
The open door light isn't even on, however, I know I'm back in business because the open door light is suddenly again shining bright as ever- but only because whatever the problem is goes away by itself.

 

Take your new battery back where you got it.
It's defective.

 

defective battery? Really? It seemed fine all winter, got it back in October.
I'd be happy if that's all it is.

 

A defective battery? Not sure I've ever heard of that happening, at least not one that goes 100% dead one minute and works the next. Your issue sounds like a bad ground actually, or a bad positive terminal connection. When the car goes dead, open the the hood, leave the drivers door open, and tap or move the connections near the battery you should be able to track down where the intermittent problem is. (you'll hear the door chime when you get a connection).

Turning on the headlights will also be a good way to tell when the connection comes back.

 

A defective battery? Not sure I've ever heard of that happening, at least not one that goes 100% dead one minute and works the next.

This happens from internal hairline fractures. Usually from one or both of the terminal posts. This can happen with cheap batteries with poor manufacturer standards or using used batteries out of wrecked vehicles.

Complete power loss can happen completely randomly or whenever heat is applied.

 

yes, it does go from 100% dead to like new in a second.
I'll check the connections, thanks.

 

i would have the battery tested.

you check all fuses? double check
doesn't happen very often but still possible ( refer to image below: )

what work has been done to the car? (recent)