I don't know what wrong with my site http://www.power-battery.com.au PR drop from PR4 to PR0 since last couple PR update and I still don't know what is wrong with mysite, can anyone give me some suggestion about how to improve my website.. waiting for your help!!! thank you.
You should thoroughly review google's rules maybe you have have accidentally violated the rules. But sometimes google does this to sites that has not violated the rules. Regardless of the reason why this happened you should be consistently building high quality backlinks, hopefully your pr will return in the future.