Powering Arduino Uno R3 with 3S 11.1V LiPo

I tested the leads of my Turnigy 1C 11.1V 2650 mAh LiPo and verified by way of a LED that red was in fact positive and black was negative. I then proceeded to connect the red lead to the Vin pin header and the black lead to the adjacent GND pin header, both on the Uno board. As I remember, all lights lit up (ON and L) and everything was OK. (I also powered the board through the barrel port using the same battery) Is this a stable way of powering the Uno R3? At some point due to an unknown cause, the light begin fading and blinking out. Now the board is dead. My question is this: will I burn up my new Uno powering it like this? Or is there some external precaution I must take to ensure the voltage regulator or whatever else doesn't get too much current? Manufacturer's data sheet says safe operating input voltage from 7-12 volts, so I am confused why my board died. Is it possible to short circuit the board by resting it powered on your hand thus connecting the solder ends on the under side of the board? Near/at the end of the boards life, the voltage regulator and ATMega328P-PU chip got very hot, esp. the voltage reg.

Any help would be greatly appreciated, thank you.

Utilize Zazen-

11.1V is quite high. Ideally you want to run as close to 7V as possible. 7v - 8V is a good range.

You can hold it in your hand, no problem.
You can power it with Vin and GND and also with the DC plug. All okay.

The voltage regulator can be too hot to touch, but it will reduce the current to prevent overheating. When it starts reducing the current, the 5V is lower, and the ATmega328p could enter a reset state or an undefined state.
However the voltage regulator will not get broken.

If this happens, disconnect everything and let it cool down, and the Arduino should be working again.

Here is the problem: The ATmega328p should never get hot. There is perhaps something connected that causes a shortcut or too much current. Is there something connected with a higher voltage to the Arduino pins, like 12V ?

Use a DC-DC converter to lower the voltage. That way the voltage regulator doesn't get hot and the 5V will be good. You can protect the ATmega328p pins with resistors (100 ohm to 10k, depends on use of pin).