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


The secret voltmeter appears to work quite well on my Arduino Uno.

When I get the time I'll play around with dimming a LED as the "voltmeter" reduces...



I think half the trouble is how they estimate the upcoming use. The might have a good handle on Ah left (but I wouldn't know if they do or not) but they seem to take the instantaneous consumption and assume you'll be doing that non-stop until it dies. So if it looks like you have a long time left, as soon as you do something intensive for a few moments, your time left drops drastically based on that heavy load.

EXACTLY! That is also valid for cars. If my car tells my I have 50km worth of fuel left, I make that fuel last for at least 70km, because I will change the way I drive. Obviously the indicator will change as well, and increase the autonomy indication, which is a lot more than Windows does calculating remaining battery time.

Like it's been said, you can get at most a fair estimate, but not an actual precise prediction.

If you are trying to calculate remaining battery time on a device for which the power consumption doesn't change much over time and doesn't depend much on how humans use it, then you can get a very good estimate. In other words, if the consumption curve for the device is known and doesn't change much, calculating remaing battery time is pretty easy.

Learn to live: Live to learn.
Showing off my work: http://arduino.cc/forum/index.php/topic,126197.0.html


calculating remaining battery time accurately is pretty hard.

What you are attempting to do is to calculate the mAH charge remaining in the battery at any given time from when the battery last had a complete charge. To do this accurately requires that one reads the actual real time current consumption continuously and keeps an accumulated mAH consumed. This is then subtracted from the rated full mAH capacity of the battery. It can be done but it requires current sensing/measuring hardware and extra software.



Predicting "remaining life" is difficult.

OTOH knowing when it's "nearly dead" isn't. Most batteries go down to about 1.1V then drop off very quickly (think "cliff").

Indeed - any you need to know the actual chemistry of the battery involved, AA cells might be Zinc/carbon, alkaline,
NiMH or even NiCd or NiZn!  Unless you know the chemistry you can't know which voltage represents the death-knell
of the cell.  For NiCd for instance its such a flat curve that in practice you can't tell, fortunately with NiMH you can
fairly well.  So you probably need to decide on a single type of cell to get a reasonably reliable indication.
[ I won't respond to messages, use the forum please ]

Nick Gammon

It's like watching a download in Windows ...

Your download will complete in 3 minutes ... wait, 5 hours ... in 4 days ... 10 minutes ... 2 hours.

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