Robot-Hat MCU is broken

Robotic kit for Raspberry Pi
1

Dear Everyone
I need your opinion.

I built a PiCrawler kit, and add a photoregister and a LCD.
It was succeeded. Next, I connected more sensors.
After I turned on the switch of robot-hat,
I2C did not react, MCU became red hot and smoke came out.

What are the possible causes?
Ex.1 Can I2C miswiring damage the MCU?
Ex.2 I use AC-adapter instead the batteries. Is it do damage to MCU?

Thanks in advance.

2

Ex.1 I2C wiring, how do you wire it, please provide a clear picture of the wiring.
Ex.2 What is your battery specification, please provide us with your battery specification or a link to purchase the battery.