Can someone post a formula / help me figure out how to figure out the battery run time for the following scenario?

I have a single 12v led light bulb with a draw of 510mA @ 12v and 1400mA @ 8v. If I start with a AGM 12v 80Ah battery and let it run for say 10 hours how do I figure out the run time given that the amp draw will rise as the battery is discharged? I know battery discharge is non-linear so I am not sure how to calculate.

Also it is worth noting that I plan on using 4 of the these light bulbs so ultimately I need to also calculate that in as well.

Battery Specs:

Product ID: 24M-XHD
Cranking Amps: 1000
Cold Cranking Amps: 800
Voltage: 12
Termination: Common Code M
Weight (lbs): 44.6
Width (in): 6.88
Length (in): 11.00
Height (in): 9.50
ReserveCapacity-25: 135.00
WET/DRY: W