Power bank 50000mAh withstands for the largest time compared to a power bank with 20000mAh. This is because if you possess a 50000mAh power bank, you will have an extra backup when compared to 20000mAh. So, if you want to select it for travel purposes, 20000mAh is more than enough. But if it is for academic or business-related purposes, 50000mAh is preferable because it requires 30000mAh to charge a laptop. These are the distinctions between these two mAhs. It is up to you to select which is suitable.