Sudden massive battery charge drain

A few more things to keep in mind. The car ISN'T "supposed" to go any specific distance on electric power only. It will go as far as it can -in the situation it is in-. That can vary a lot!

You can NOT feel what the car is doing all the time. Ask all the dead aircraft pilots why they didn't pull up as they approached cumulus granulitus. They "thought" they WERE climbing. Human perception is VERY unreliable.
A classic example for Prius drivers is the wheel slip braking switch we get. A lot of drivers claim the car accelerates forward. It does not!

The battery has about 6.5 A-hr of capacity. That isn't much! To make that worse, the HSD only uses about 40% of that. It runs the battery from about 40% charge to about 80% charge. It even tries very hard to just run it over about 15% charge, around the 60% level. You can force it over and under the 60% level in "normal" driving but it fights to get it back to where it wants it. So you typically get to use about 20% of the capacity in normal driving. That's 1.3 A-Hr or about 260 W-hrs. That isn't enough to drive anywhere!
It isn't an "electric car", it's a hybrid that runs on gasoline and uses the electric part to enable the engine to run at peak efficiency.
Finally, the "charge meter" we all think we can rely on is also very unreliable. What it reads can change overnight when the battery is fully disconnected!

 

if the car is already warmed up and is turned off and then turned on, then depending on how hard the pedal is pressed it may just use electric power only. i experience this when i fill up at a gas station right next to the highway, since I then have a long strech of road without stopping; if I generally keep it in the middle of the PWR section more or less, I can feel that the enigne does not rev up and I see my MPGs being higher than usual, in addition to the battery dropping really fast. The end result is either I press enough on the gas to get the engine to take over or the battery goes to 2 bars and then the engine kicks in.

If this happens again, keep an eye on your instant MPG meter. You may notice that it may be higher than usual given your driving conditions. Eventually the engine will be used and you're see the drop in MPG. I suspect this is what is happening. This is normal operation; nothing to be worried about.

I don't know why the car this, but I think it has something with reducing emissions. Similar behavior I believe would be seen from a cold start, though since most of us don't live by a long stretch of uninterrupted roadway, we don't notice the car using mostly electric power at first.