Laptop Battery: Original vs Chinese

My Acer Travelmate 4020's battery is almost dead. I'm being offered the original battery for 4500 INR and the compatible ones for 2500 INR, and thats around half the price of the original ones.

I wanted to know how bad the chinese battery could be so that I can make a decision. Are they really inferior or they're just being underated? Please share your experience if you've used a non-original chinese battery in your laptop. One more Important thing I wanted to ask is about their safety, I hope they won't explode/melt if I go away leaving the charger plugged in.