[Katsunami]

As said in the first reply: if the voltage is close AND the connections on the battery are correct, nothing bad will happen. It is how the third party batteries are made; just by approximately copying the original.

Actually, sometimes batteries are interchangeable. For example, the Fuji X100 digital camera uses the exact same battery as my Ricoh GXR-M. You can't really find any third party batteries for the Ricoh, as it is not a well known camera, but you can find plenty for the Fuji.

More mAh will make your battery last longer though. It's just how much power it can store.

You probably wouldn't need the screws; you could basically tape the battery in place. It's done that way in quite some mobile phones.

What psycholoner said is also true though: you'd need to get a battery that has a good protection circuit to keep it from overcharging, etc. As far as I can see, there are many third party Kindle batteries around, but I don't know if they can be shipped to your location.