@alexvalles, cell phones nowadays are not made to be user-friendly; the days of being able to pop off the back of the phone and slide your thumb in the notch to remove the battery are long gone.
That being said, there are no phones where it is impossible to replace the battery, but the degree of difficulty varies widely, depending on the phone.
So despite your assertion that your battery cannot be taken out - it can. If you will provide the model number of your phone, there's a fair chance myself or one of the many other contributors here on this site can find a set of instructions that will show you how to replace your battery yourself.