A very small user of power is a 1.2 watt LED light running on a 12 volt power source will use 1.2W / 12V = 0.1 amps. Therefore a 100ah (amp hour) battery will last for

**1000 hours**. A slightly different example is a 60 watt fridge running on a 12 volt power source uses 60 /12 = 5 amps, but only while the motor runs.Thereof, what is an amp hour?

Chapter 11 - Batteries And Power Systems. A battery with a capacity of 1

**amp**-**hour**should be able to continuously supply a current of 1**amp**to a load for exactly 1**hour**, or 2**amps**for 1/2**hour**, or 1/3**amp**for 3**hours**, etc., before becoming completely discharged.How many watts are in an amp hour?

Power in Watts = Current in Amps x Voltage. A battery rated for 100 amp hours will provide 5 amps for 20 hours. If we have a

**12**volt battery, we multiply 100 by**12**and determine that the battery will provide**1200 watt**hours.How are amp hours calculated?

The key is to use the watts you know to

**calculate**the**amps**at the battery voltage . For example, say you want to run a 250 watt 110VAC light bulb from an inverter for 5**hours**.**Amp**-**hours**(at 12 volts) = watt-**hours**/ 12 volts = 1470 / 12 = 122.5**amp**-**hours**.