9V alkaline batteries and drawdown time.

[rogervan]

I need 18 volts at 100 mA. How long will it take to drain these in-series batteries? Let's say, how long until the output drops below 100 or 90 mA.

Rog

 

[donkey]

it depends on your 9v.
from my memory (which is fractured so please be nice if I am wrong) its aroud 550mah. if you draw 100 ma per hour you'll get 5.5 hours in total. having said that it'll probably drop after 3-4 to a voltage below that which most circuits can use

 

[KJ6EAD]

Here's the data sheet for the Duracell Coppertop 9V battery (MN1604).

http://www.duracell.com/media/en-US/pdf/gtcl/Product_Data_Sheet/NA_DATASHEETS/MN1604_US_CT.pdf

 

[donkey]

oh also having 2 9volts in series will produce 18volts at about 550mmah.
if you upgrade to 12 AA or C or D batteries then you get more amp hours thus giving your project a longer life.

http://www.batteryweb.com/pdf/inverter_battery_sizing_faq.pdf shows a basic setup of solar but can be used for any power setup.

figure out what amp hours you have and divivde by the amps you are using (the load) and you will get a figure that shows roughly how many hours it will run for.
9volt batteries are the worst for amphour rating as they are producing 6 times the voltage of an AA battery but only double the size, something has to be small to make it work

 

[CocaCola]

(volt batteries are the worst for amphour rating as they are producing 6 times the voltage of an AA battery but only double the size, something has to be small to make it work

A bunch of 1.5 volt button cells or 6 AAAA usually, not much to brag about as far as mAh are concerned...