With the help of something small, open the battery compartment.

If you see now where the battery resides, you will see one screw.

But there is another one hidden under the gray piece of plastic. So we need to remove it.

I used the tip of a dental pick.

Now you can see the second screw.

Undo the two screws and you can now liberate the internals in two pieces.

Without taking out completely one of the screws, push against it so the upper part slides out. You can now grab it with you hands and put it aside.

Now, pull the bottom part.

We have only one step to do to consider the teardown complete.

Undo the four screws holding the main board with a #00 phillips screwdriver.

Now the teardown is completed.

To reassembling it, we should take special care on the battery contacts are they should be springy and put under the gray bottom plastic.

Bend the contacts a little bit to make this shape.

Insert the top part, this step is easy.

Now insert the bottom part, but half way.

And, with the help of something slim, push the bottom completely making sure the battery contacts are behind the gray plastic.

In the picture I show you how NOT to let the contacts, it is outside the gray plastic.

Now, screw the two screws (the shorter one is the one that is going to be covered by the spring of the release mechanism).

Put the spring + the plastic pusher into place.

And put the black top cover in place, taking special care on align it so this part is in the IR led side.