Not sure what you need help with, but if you're trying to power down your phone and the power button is not responding, you'll have to wait until the battery is depleted (since you mention the removable battery).
If the phone has charge but the button isn't responsive, there's no other way to turn it back on without a button repair.
Similar case if your battery isn't holding charge or is otherwise damaged; without a physical repair, not much you can do.