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Topic: How to estimate number of hours remaining before battery dies? (Read 1 time) previous topic - next topic

kurtselva

Hi guys,

I am doing a battery life indicator for a device. A red led will light up when the voltage reaches below a certain limit, which is at least 2 days before the AA battery fully dies.

As such, I want to know how to determine the number of days left before a AA battery dies. I have attached the datasheet for a AA battery but it only shows the constant current performance chart. My device draws around 50ma current for about 10seconds, 4 times a day, when a motor rotates. And all along, it draws a current (ard 1ma I think) when it runs a timer.

So, how can I determine the voltage when the battery is abt 48hours before "dying"?

vasquo

Find out the mAh of your battery brand/type and compute accordingly.

There is a wide range though for AA battery types. Anywhere from 400mAh to 3400mAh.
http://en.wikipedia.org/wiki/AA_battery

and even then, what you'll come up with is a best guesstimate. Temperature, efficiency, losses will also come into play and affect battery life.

JimboZA

It's a bit like tightening a nut without a torque wrench.... do it up till it strips, then back it off a bit  8)

(ie, run the battery flat then you'll know....)
Roy from ITCrowd: Have you tried turning it off an on again?
I'm on LinkedIn: http://www.linkedin.com/in/jimbrownza

Nick Gammon

Judging by the chart for the remote, once you are down to 1V it's probably time to replace it.

There are so many factors (like the temperature) that you probably can't be much more specific than that.

(edit) Maybe 1.1V

Grumpy_Mike

Have you noticed how wrong your laptop or tablet gets this. They have vastly more engineering resource than you and they can't get it right. It is not something that ca be accurately predicted. There are too many variables.

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