# amp question

by david90
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 P: 303 How long will a device drawing 8 mA last on a 12 v bat that has a 25mAh? 25/8 = 3.125 hours?
 PF Patron Sci Advisor Emeritus P: 10,400 You got it. - Warren
 P: 303 is there a bat as small as a watch bat that can produce that much mAh at 12v?
PF Patron
Emeritus
P: 10,400

## amp question

Not that I know of.

- Warren
 P: 303 what is ur mAH for watch bat?
 PF Patron Sci Advisor Emeritus P: 10,400 Hell if I know, but I've never seen a 12V watch battery. Most battery chemistries in use today are 1.5 volts or so -- they'd have to pack 8 cells into that watch battery package to get 12V, and I don't think it's been done. - Warren
 P: 1,309
P: 1,309
 Quote by david90 How long will a device drawing 8 mA last on a 12 v bat that has a 25mAh?
Voltage is electrical pressure, and it is analogous to water pressure. We don't need to know what the voltage is to answer this; we just need to know that it is considered consistent throughout the problem. The question should be stated as:How long will a device drawing 8 mA at a particular given voltage last on a battery that has a capacity of 25mAh at the same given voltage?.

 25/8 = 3.125 hours?
Yes, if the question is stated as I corrected above.