I have this gun and while it's a solid AEG, I agree that removing/replacing the battery is a PITA... until you get the hang of it.
The trick is to remove the entire crane stock and disconnect the battery (fish the battery wire out of the buffer tube with a fork or something). When reinserting the nunchuk battery, try to coil as much of the battery wire in the buffer tube as you can before replacing the crane stock (with the battery in it). This will (hopefully) allow you to adjust the crane stock the way it should.
It takes some trial and error, but I feel your pain. The important thing is to not force it or anything when you feel resistance upon reinstalling the crane stock; just take the whole thing out, rearrange it, and try again. Forcing it will only strip the wires, and potentially ruin your battery.