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I know that an Amp Hour is 3600 C

I know that a Watt is a Joule / s

I know that 1 J= 1C/V

3600 C * 120

So the initial energy stored in the battery is (3600*120) / 12V=36000 Joules

29 Watts=29 J/s

So this battery is delivering 36000 Joules at a rate of 29 J/s

36000/29 = 1241 seconds.

This is only about 20 minutes. This seems very short. I use 7Amp hour batteries at work. I've used them to power a light for a few hours.

So my intuition tells me this answer can't be right.

How much charge flows through the battery during this time? : I=Q/t = 432000 C / 1241 s = 348 Amps. But this assumes I got the seconds correct.

Did I do this right?