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**battery life**of a 12v

**9ahbattery**

**9ah**= 108 watt hours, so 108/20w = 5.4hours.You probably want to test it if its important though,since

**battery**specs

**can**be depend oncertainconditions.

Hereof, how long will a 40ah battery last?

**Long** answer: If the power output was not at 12v, then we**would**reverse the power equation to **do** 12*40 = 480WH.This meansthe **battery can** provide 480 Watts for 1 hour.**40AH**(Amp Hours)/4.16Amps = 9.6 hours, or 9 hours and36minutes.

**long**your

**batterywilllast**,

**calculate**the

**battery's**total capacityanddivide it by your circuit's power. Multiply the

**battery's**reserve capacity by 60. With a reserve capacity,for instance, of120: 120 x 60 = 7,200.

Simply so, how long will a 200ah battery last?

The **200AH battery can** feed 200 Amps for 1 hour,or100 Amps for 2 hours, or 10 amp for 20 hours.

Though not designed for deep-cycle applicationswithoutthe car's engine **running**, a typical 450 watt-hourcarstarting **battery should** be able to safely power aportableDC 1.5-amp **TV**/DVD player for about 12 hours or a31″flat screen (156-watts) for about 45-60 minutes and stillbe ableto start the car's engine.