Battery Indicator: How to Measure Remaining Energy

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Discussion Overview

The discussion revolves around methods for measuring the remaining energy in rechargeable batteries used in various electronic devices. Participants explore the accuracy and techniques involved in real-time energy measurement, touching on both theoretical and practical aspects.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants mention two main methods for measuring battery energy, though specifics are not detailed.
  • One participant suggests that understanding the context of the question is important, particularly if it relates to schoolwork.
  • Another participant expresses curiosity about the general workings of battery indicators without a specific battery in mind.
  • A participant proposes that a V-Ah characteristic curve might indicate remaining charge, but acknowledges that voltage also varies with load, complicating this approach.
  • It is noted that the voltage drop when a battery is drained may not provide precise measurements for remaining charge levels.
  • One participant discusses tracking current and time as a potential method, along with measuring battery voltage, while emphasizing the importance of battery chemistry in determining accuracy.
  • A suggestion is made to consult battery datasheets for voltage characteristics under different loads.
  • Another participant mentions that some battery indicators provide an expanded voltage scale but cautions that these readings may not be entirely reliable.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the best method for measuring remaining battery energy, and multiple competing views and uncertainties are present throughout the discussion.

Contextual Notes

Participants highlight limitations in measurement accuracy due to factors like load variation and battery chemistry, as well as the need for specific data from battery datasheets.

Jiggy-Ninja
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Pretty much every single electronic device in the world with an internal, rechargeable battery (MP3 player, phones, handheld games, etc) has some way of measuring how much energy is left in the battery.

How do you measure the remaining energy in real time like that? How accurate are those methods?
 
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Jiggy-Ninja said:
Pretty much every single electronic device in the world with an internal, rechargeable battery (MP3 player, phones, handheld games, etc) has some way of measuring how much energy is left in the battery.

How do you measure the remaining energy in real time like that? How accurate are those methods?

There are two main methods that I'm aware of. What is the context of your question? Is your question related to schoolwork? If it is, you need to tell us your thoughts on the subject before we can guide you to the answers. Even if it is not directly schoolwork, you should be able to post the results of your research so far.

Hints -- (1) pull up some datasheets on the batteries you are asking about. (2) How could a charging circuit measure and remember energy transfers...?
 
berkeman said:
There are two main methods that I'm aware of. What is the context of your question? Is your question related to schoolwork? If it is, you need to tell us your thoughts on the subject before we can guide you to the answers. Even if it is not directly schoolwork, you should be able to post the results of your research so far.

Hints -- (1) pull up some datasheets on the batteries you are asking about. (2) How could a charging circuit measure and remember energy transfers...?
Not schoolwork related, just one of those "I wonder how that works?" situations. So I didn't have any specific batteries in mind, just wondering about some ways that it's done in general.

I did some googling, but the results I got were stuff like timing how long the battery takes to drain to figure out the full charge, which obviously doesn't happen for the indicators I'm thinking of. I don't quite know the right magic words to search for to pull out the answer.

My first thought was that there might be some V-Ah (Volt -- Ampere-hours) characteristic curve for to battery, ie the voltage changes in a slight, predictable way depending on the remaining charge in the battery. But then I remembered that the voltage would also vary with the load so that's no good.

I know that when the battery gets drained too far the voltage can drop pretty significantly, but that's not precise enough for something to measure, for example, that the battery is 75% charged.
 
Jiggy-Ninja said:
Not schoolwork related, just one of those "I wonder how that works?" situations. So I didn't have any specific batteries in mind, just wondering about some ways that it's done in general.

I did some googling, but the results I got were stuff like timing how long the battery takes to drain to figure out the full charge, which obviously doesn't happen for the indicators I'm thinking of. I don't quite know the right magic words to search for to pull out the answer.

My first thought was that there might be some V-Ah (Volt -- Ampere-hours) characteristic curve for to battery, ie the voltage changes in a slight, predictable way depending on the remaining charge in the battery. But then I remembered that the voltage would also vary with the load so that's no good.

I know that when the battery gets drained too far the voltage can drop pretty significantly, but that's not precise enough for something to measure, for example, that the battery is 75% charged.

The two I was thinking of are the keeping track of current and time, and measuring the battery voltage. Depending on the battery chemistry, you may or may not be able to tell the % remaining from the output voltage. The battery datasheet should show the output voltage as a function of time for various output current loadings (multiple curves).

BTW, I just googled Battery Discharge Calculator, and got some interesting hits. Check out the hit list to see if it helps:

http://www.google.com/search?source...L_enUS301US302&q=battery+discharge+calculator

.
 
The ones I have seen just give an expanded voltage scale.

So, for a NiCd battery, they give 1 volt as the minimum reading and 1.3 volts as the maximum reading but calibrate it as 0 to 100 % capacity.

Better than nothing, but you can't take the % reading too seriously.
 

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