Motorola BX40 Battery for Mobile

Have this battery for my older Motorola MOTORAZR phone bought since no longer the old battery lasts very long. However, the battery should be slightly thicker than the original battery, because the back does not close 100%. Unfortunately, there remains a very small gap.
In addition, the battery in the cell phone does not stop at a lot longer than the old battery. But of course, the mobile phone is already a classic car and therefore the battery will it no longer be so good.