How Can I Calculate Battery Discharge Time Using a Formula?

[abhipatil419]

Hi guys!
For a school experiment we are supposed to connect a 9v battery to a 180 ohm resistor and multimeter and calculate how long it take to die at different temperatures .
does anyone know how can i do this using a formula? I will need it in my report.

Thanks for the help! :)

 

[.Scott]

It sounds to me as though they want you to find the formula by performing the experiment.
How many temperature values will you be using? What voltage value are you using as the threshold for a "dead" battery?

I would think that you would use at least four 9V batteries, allow each to settle on one of four well-measured and well-distributed temperatures, check them periodically for "death", and measure and record the time.
The plot the results and fit a formula to them.

Using a Duracell and "death" at 0.1V at 50mA, expect you timings to be in the 5 to 8 hour range.

 

[abhipatil419]

Hey Scott!
I have already conducted the experiment today with 3 diff. batteries at 3 temperatures : -22 C, 24 C and 35 C
the resistance was 180 ohm
the voltage cut off was 7 volts

I am having trouble producing a formula that fits

 

[.Scott]

What were you times? Is there approximately a linear relationship or is it more complicated?

 

[abhipatil419]

Here you go :)

 

[Nugatory]

Here you go :)

Hmmm... 14 minutes between .Scott's post and your reply suggests that you didn't spend any time thinking about what @.Scott said. Let's try this again:

Is there approximately a linear relationship or is it more complicated?

 

[.Scott]

According to the text on your plot, the temperatures are -22, 25, 47. According to your post, they are -22, 24, 35.
If it's -22, 25, 47, a linear approximation is probably not good enough. You should collect more data - say at 2 and 36.
If it's -22, 24, 35, use the linear approximation. What kind of "best fit" methods are you learning about?