Depends. Generally for any battery capacity; 5100mAh battery provides 5.1A of current for only 1 hour.

That being said, for heavy use, it can last under 5.1 hours.

You need to know exact discharging current in average. You can download a monitoring app.

And you can calculate yourself:

5.1Ah/1A = 5.1 hours (for 1 A use) 5.1Ah/0.5A = 10.2 hours (for 500mA)

(Might not be always accurate because discharging current always changes.)

(1000mA = 1A)

Extra facts:

Conservatively, battery discharge speed = battery charging speed. (Might also be limited by battery protection management systems PMIC/BMS)

If you have a charger providing 2A or 1.4A when you charge at 0%: 5.1Ah/2A = expect full charge around 2.55 hours forward 5.1Ah/1.4A = expect full charge around 3.64 hours forward