You're right, I mangled Ah and Wh in my head, sorry. 4V 1Wh battery and 24V 1Wh batteries are equally useful.
Your numbers are a little bit off though. I just googled some power bank (which is supposedly better than smartphone). It claims to provide 20 000 mAh at 5V. So it's 20 Ah at 5V or 100 Wh. I think most smartphones are around 10-20 Wh. Far from 5 kWh. But this discrepancy was already noted in other comments.
Your numbers are a little bit off though. I just googled some power bank (which is supposedly better than smartphone). It claims to provide 20 000 mAh at 5V. So it's 20 Ah at 5V or 100 Wh. I think most smartphones are around 10-20 Wh. Far from 5 kWh. But this discrepancy was already noted in other comments.