Even if you have done online check in, you should reach KLIA 2 before 10.50pm (30 min earlier min) as the customs are relatively slow and the distance to boarding gate is very far.

It is available at any convenience store / mart in KLIA / KLIA 2 at around 0.50 - 1.00

Based on my experience, for China, Beijing capital was the strictest where an officer looked at my power bank carefully and read the label on it.

Shanghai and Hainan Island is less strict. An officer just had a look at it and read the label for few seconds.

Not sure about power bank without label / label without indication of output but I would assume it would be confiscated at Beijing.

For other countries, for the countries i've visited in the last 2 years (around 15), generally western countries are stricter than eastern countries (but not to the extend of Beijing). They will read the label and look at the power bank for few seconds while eastern countries officers did not even touch it.