What is the correct way of measuring remaining battery capacity?

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Discussion Overview

The discussion revolves around methods for measuring the remaining capacity of batteries, particularly in the context of using Arduino and other electronic components. Participants explore various approaches, including voltage measurement, battery fuel gauge ICs, and the implications of battery chemistry on capacity estimation.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning
  • Experimental/applied

Main Points Raised

  • One participant suggests measuring battery voltage using an Arduino's ADC but critiques this method for its limitations with batteries over 5V and those with flat discharge curves, like LiPo batteries.
  • Another participant mentions the necessity of a nonlinear discharge curve for accurate measurement, particularly for LiPo batteries.
  • Some participants propose using battery fuel gauge ICs that monitor charge and discharge cycles for a more accurate representation of battery state.
  • A participant discusses the Nernst equation as a theoretical framework for understanding battery voltage but notes its practical limitations.
  • There are suggestions for using op-amps to adjust voltage ranges for ADC readings.
  • One participant shares their experience with a simple charge indicator for a lead-acid battery, using an analog voltmeter and a Zener diode.
  • Another participant describes a battery monitor that integrates watts over time but emphasizes the need for user input regarding battery capacity.
  • Concerns are raised about the risks of overcharging lead-acid batteries and the reliability of direct connections to solar panels.
  • Some participants highlight the importance of measuring voltage after a resting period to avoid inaccuracies caused by current flow.
  • Discussions also touch on the differences between battery chemistries, such as lithium and lead-acid, and their respective charging requirements.
  • One participant notes that while voltage measurement is common, it can be inaccurate due to factors like current draw and temperature affecting battery capacity.
  • Another participant mentions the importance of limiting discharge to prolong battery life, sharing personal experiences with solar-powered systems.

Areas of Agreement / Disagreement

Participants express a variety of views on the best methods for measuring battery capacity, with no clear consensus on a single approach. There is acknowledgment of the limitations of voltage measurement, but differing opinions on alternative methods and their effectiveness remain unresolved.

Contextual Notes

Some participants note that the accuracy of battery capacity measurements can depend on factors such as current draw, temperature, and the specific chemistry of the battery. There are also references to the need for user-defined parameters in battery monitoring systems, which may introduce variability in results.

Who May Find This Useful

This discussion may be useful for hobbyists, engineers, and anyone interested in battery technology, measurement techniques, and the practical applications of electronics in energy management.

  • #31
A major issue here is the definition of a discharged or uncharged battery. ... And I am really surprised at the way that battery discharge is being described now compared to how it was described 30 years ago.

Traditionally, batteries were considered "discharged" when they could not longer power the device they were powering. So whether a battery is "discharged" or "fully discharged" isn't exclusively depended on the internal battery state - the load it is expected to support is also part of the "discharge" condition.

Playing with Google for a few minutes hasn't turned up that definition for me - but it use to be topic one in any discussion of battery life or battery charge condition. Certainly part of this change reflects that modern rechargeable batteries are often used in devices with very wide load ranges. If you're running GPS apps on you cell phone, the battery drain and the discharge point will both be higher than if you only are playing sudoku.

Still, if you are expecting your device to continue functioning until your battery meter goes to zero, don't expect any off-the-shelf solution to work. You will need to match your meter to your whole device - not just the battery.
 
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  • #32
There are also methods based on measuring the AC impedance of the batery. The AC impedance relates to the state of charge while the frequency where the impedance is measured is still a degree of freedom.
 

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