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Topic: How to estimate number of hours remaining before battery dies? (Read 4766 times) previous topic - next topic


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.

It's been my experience that Nicad and MiMH have very similar flat discharge curves where the terminal voltage does not give you a good indication of remaining charge until it's almost at the end.




Remember all those milliamps are in relation to milliamp hours. So, the 1 ma timer draw = approximately 25 ma in a day. The 50 ma draw is only happening 40 seconds out of an 86,400 second day. A 2500 ma battery will last least a month.  Your mileage may vary!


So, the 1 ma timer draw = approximately 25 ma in a day.

You mean....

25mA hours

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Your answer may already be here: https://forum.arduino.cc/index.php?topic=384198.0

Nick Gammon

So, the 1 ma timer draw = approximately 25 ma in a day.

You mean....

25mA hours

In Australia, it would be 24 hours in the day. YMMV.
Please post technical questions on the forum, not by personal message. Thanks!

More info:


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"?

you need battery monitor IC which support Battery Fuel Gauge/Gas Gauge.

one sample from ST;-

make sure select IC type match with battery type.

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