Can I change the battery of a fake Iphone 4s? (Chinese Clone)?

I have recently bought an iPhone 4S Clone exactly the same with the iPhone 4S:

-Screen Size is almost the same.
-Battery is built in and you can only open the back panel using philips screw driver
-Uses the same cable and USB from iPhone
-The SIM is also located at the side panel (Not like those other clones that opens at the back) using the pin to eject the SIM
-Uses the same and almost exact User Interface (I think 89% cloned U. I.) Messaging, Options etc.
-Has pre-isntalled apps like Fruit Ninja (crappy LOL), Slide-to-Peek Girls (Chinese Perverts made this app LOL), Plant Corpse - Plants Vs Zombie (I've played this and I think this game/ app is the most decent one I've found)
-Java program called "JBLEND"
-Wi-Fi -yay!

overall - 88-90% clone accurate.

Now back to the question. If ever I wanted to change the battery of this iClone Phone, Can I buy after market parts? Or can I use the same battery pack used by iPhone 4s?

You can't really buy a battery pack for the iPhone 4S because in the real model, it is not a replaceable part. Although you may be able to replace it in the clone phone, you may not even be able to obtain one. If you are planning to replace the battery, I would go with the same model that is currently in your phone.

People with real iphones are losers
people with fake iphones are super losers

get real phone
get a Note 2

As for me - I can see 3 ways of making the right decision.

1). When your battery will die, you should find a service-man who works with China-made phones and ask him for repair/change your battery. And believe me - it's not so easy. Most services don't want to take Chinese phones and/or accessories for repairs. (But you may find a specialist who is near your place of living on such place as special forum like "black forum" (you will find a link below).
2). Or, if you bought your phone from a big reseller, you can speak with him and ask a question about "after sales" offers. If you get a positive answer, then you better buy the second battery as soon as possible, because after year or two you may meet with situation that it's impossible to find a new battery because no one is producing it…
3). Another way, when your battery life will come to its end - you may probably buy a new phone. I know a lot of people who doesn't like to have the same phone more than 1 year.