calculation

I was reading datasheet for module RF96 (datasheet attached), I understand that we have to set register values to set carrier frequency as descrubed on the page 103, this is also described at some other parts of the datasheet like Pages, 13, 53, 77, 88 Formula described to calculate...

I have a 8 AA batteries (12V total) that is powering a light that draws .0517A. The light no longer outputs enough light when the battery voltage drops to 8Vdc. Typically I'd calculate battery life via: 2.5Ah * 8 = 20AH. Then: 20AH/.0517A = 386 hours. Does this equation change if I want to...