My daughter pulled into a friend'* driveway and my wife'* 2006 Cad DTS when it started running rough. There was a notification that the charging system needs service, then it suddenly died. I came out to check it and found I was unable to turn the key to the completely off position. I tried to restart with no response. Dead gauges, etc. The battery was doornail dead. I turned the key on all the way again so I could put the car in neutral, but the shift lever would not come out of park and still could not turn the key to the full off position. Even with the key in the run position, the steering wheel was locked. I got out and found the gas filler door had popped open. Odd, because our daughter doesn't know how to put gas in a car, but I closed it.

I charged the battery, started the car - it ran rough, had the same charging system service required notice, I put the car in reverse to back it up but after 10 seconds, it died again, Again, the gas filler door had popped open and the battery was dead. No gauges, etc.

I closed the filler door, I got a ride to my house and got my F-250 and trailer, checked battery voltage, which turned out to be 11.3V, which apparently isn't enough to move the gauges. I fully charged the battery again. I returned to the Caddy with the battery, plus another one out of my 2000 Mustang. I put the smaller Mustang battery in started the car and backed it up 20 feet to where I could almost load it onto the trailer before it died again. I closed the gas filler door and put in the original Caddy engine, started the car and decided to drive it the 100 yards to the road and another 40 yards downhill on the road before it died. Same symptoms, Being at the bottom of a swale, it was a bad place to try to load onto the trailer, so instead I closed the gas filler door a third time and walked to my F250 and drove it the 8 miles to my house to recharge the batteries. I returned to the car, started it with the freshly charged battery and drove like hell about 1/4 mile to a level spot on the dirt road at the top of the hill to load it onto the trailer. I kept it in neutral knowing it would not come out of Park if it died first. I noticed this time that there was a service notification that power steering maintenance was required. I loaded the dead car onto the trailer and took it home. After positioning the trailer and charging the battery, I cranked it up and drove it off the trailer. Before turning the key off I again noted the charging system and power steering maintenance required notifications. I closed the gas door and disconnected the battery which I am currently charging it again so I can roll up the windows. Looks like rain.

When I reconnect the battery after charging there is a pretty solid spark, but I attribute that to the key being stuck in the acc position when it dies (at which point it won't turn completely off). When it dies and I remove the grounding cable I find the terminal clamp fairly warm to the touch, while the positive cable terminal is cool. The dealer changed out the fuse/relay box under the seat about a year ago and everything seems ok there.

Thoughts? Prayers? Last rites? Such a strange combination of symptoms, especially the gas filler door. I don't even know what to look at first.

It blew the gas cap through the fuel door?
Why don't your start with a new battery? That battery may have an internal short which is causing all these problems.

The gas door has never done that before. The second time it happened, I checked to make sure the cap was tight, which it was. I still have no logical explanation. As for the battery, I'll take it in to have it checked, but I can charge it and leave it overnight and it will still maintain a charge. When I reconnect it, there is a pretty solid spark that jumps across from the terminal cable to the battery post; it;* like a short from an unfused wire/cable, although it isn't strong enough for me to believe it is a direct short, but is enough to drain the battery within about a half a minute.

I'm really really curious how old the battery is.

Next time it is running, check the charge voltage and report back.

It might be dying because the battery is toast and you're hitting the brakes (therefore creating a voltage drop inrush of current to the brake light bulbs). My LeSabre does that when the battery is toast or when the side-post terminals are loose.

If it'll drain the battery in 30 seconds it'* a dead short. Also, you can have a shorted cell. The only true test is to load test that battery.