# Battery Life (switching vs Linear Regulators)

#### keyboardcowboy

Joined Dec 31, 2012
25
how does using switching regulators in place of linear regulators effect battery life??
If i use a 7805 to get 5v from 12v (2 Ah) battery consuming a current of 500mA, the battery should last 2A/0.5A = 4 hours RIGHT???, the thing that i do not understand is that the linear regulator is wasting the other 7v in the form of heat, shouldn't this effect the battery life as well??

#### Shagas

Joined May 13, 2013
804
The thing is that when you pull 500mA of current from a 12 volts battery , you are pulling in effect 12 x0,5 = 6 watts of power . Now you can choose what you will be doing with those 6 watts of power .
The voltage regulator wastes 7 x 0.5 = 3,5 watts and there is 2,5 watts available on the output of the regulator .
Basically the battery life is determined by the current pulled from it (in this case 500ma)
It also provides 12 volts , now if you use the full voltage or not is your problem , not the battery's (at least this is how I like to think of it )

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#### Shagas

Joined May 13, 2013
804
also when I say 'use the full voltage' I mean it in the sense that if you connected the battery say directly to a motor which pulled 500ma then the motor would be using all of the 6 watts provided by the battery .
If you are using a regulator to give you 5 volts then you are in essence 'wasting' 7 of the volts that the battery provided .

In this specific example lets say you had a 12v 2Ah battery and a 6V 2Ah battery .
Both batteries would have exactly the same life span. The only diffrence would be that with the 12v battery 3,5 watts would be wasted in the regulator and with the 6 volt battery only 1/2 watt would be wasted in the regulator .

#### #12

Joined Nov 30, 2010
18,210
I think shagas missed the point. A switching regulator can be in the range of 90% efficient. 12 volts times 1/2 amp with a linear regulator will take 6 watt hours per hour out of your battery. A 5 volt load at 1/2 amp is 2.5 watts, and the switching regulator will use about 2.8 watt hours per hour to do the job.

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#### crutschow

Joined Mar 14, 2008
25,267
Just to make it clear to the OP as to how this higher efficiency of a switcher helps, a switching buck regulator that reduces the voltage from input to output will take less input current from the battery then it delivers at the output. It rather acts like a transformer to simultaneously reduce voltage and increase current at high efficiency. That is how it improves battery life over a linear regulator.