How Long can a Battery Power CFL Bulb?

How long could a fully charged 12v battery power a 80watt cfl bulb?
- Ty (age Jon)
Cali

I'm guessing you mean a lead-acid car battery. They vary quite a bit in how much charge they can deliver, but 40 Amp-hours is a fairly typical capacity for low-current use. A bigger question concerns that CFL bulb. Does it realy use 80W or is it an "80W equivalent" bulb, which would use only about 20 W? I'll guess the latter.  Since 40 A-h at 12.5V is 500 W-h, at best that 20 W CFL could run about 25 hours. Since the battery supplies DC and CFL's require AC you need a DC to AC inverter, which will waste a bit of the energy, reducing the run time further. 

One practical improvement would be to use 12V LED lights. These require no inverter and also are typically a little more efficient than CFL's. Thus for a given battery and desired light level you could run a bit longer and have a simpler set-up. 

Mike W.

for background questions: 

(published on 12/06/2014)