Sorry if this is in the wrong section (it isn't homework). I am trying to form a basic understanding of electricity. Right now I'm attempting to figure out how to calculate how long a battery will last with certain devices.(adsbygoogle = window.adsbygoogle || []).push({});

I might be completely off base but here's what I've got.

12volt battery rated at 250Ah

Device is rated at 115volts 10000 BTUs, that's 2931W-h

2931 / 12 = 244 amps (97.7% = of battery capacity)

--

Likewise

Battery capacity 12 x 250 = 3000watts

Using 2931 in one hour is 97.7 %

Not sure if this is correct was picturing a car battery and a portable ac unit

......one other

Battery rated at12volt and 12Ah

Device 1420mAh (iphone)

12000mAh battery at 12 volts

12000/1420 = 8.45

Does this mean I can charge the iphone 8.45 times off the other battery?

Also is there any calculation required when using a power inverter? (I would be using a power inverter to go from dc to ac in these examples. (Not that id ever want to power a 10000btu ac unit in my vehicle lol)

Thanks

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# How to calculate how long a battery will last

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