How to open the iPod Nano case

Hi, this is an update because I have exchanged the batterie by myself now.
First of all I would like to highlight that I have studied electronics and am familiar with opening and repairing electronic gadgets of any kind.

The soldering process of the three tiny wires (white, red & black) was the smallest problem. The new batterie holds the power now the way, you would expect from a brand new iPod Nano. That was the good news.

But all my efforts to take precautions, to be as careful as I could possibly be, failed at the end.
Despite having used the necessary tools, the casing of my (as-good-as-new) iPod Nano 3G has suffered considerably.
The frame is scratched, bent and the brackets don't allow the rear side to be closed tightly anymore.

Now I end up with a fully funcional iPod Nano 3G which I really loved, until the day the batterie has been exchanged.
Why is Apple unable to produce mp3 player, meeting the long term needs of their owners ?
We all know that batteries are worn out one day. It would have been simple, to enable the rear side to be removed more customer friendly and actually it would not require the battery to be soldered at all.

Sorry, but I'm just very disappointed about the destroyed casing of my iPod, despite having been ever so careful.
And while I'm at it, I also cannot understand why Apple does not allow iPod users to extend their gadget's memory with microSD cards.