Electronic – read smartphone batteries gas gauge info with a PIC

batteriesgaugepic

I'm in a quest trying to find some easy way of having my batteries charge level displayed. I've found it not so trivial as I thought it would be (because any smartphone is capable of doing that). Than it hits me, it must be something to do with theirs batteries.

I've learned some models of battery have one or two terminals for communication to an gas gauge integrated inside the battery package.

So the question is, are those terminals easy to be read? If I decide to use that kind of battery in my project, can I read that gas gauge with a PIC? What kind of protocols are used normally for that communication? Do OEMs give that kind of info?

Does anyone knows where to find that? Any datasheet. I could not find anything actually on the web.

Best Answer

Here is an excerpt from an article I found:

"To determine the available charge in a battery, simple monitoring methods are preferred. They should consume little energy and should (ideally) allow one to deduce the charge level from battery voltage. Such a voltage-only method can produce unreliable outcomes, however, because no clear correlation exists between voltage and the available charge (Figure 5). Battery voltage also depends on temperature, and dynamic relaxation effects can cause a slow increase in the terminal voltage after a reduction in load current. Thus, purely voltage-based monitoring is unlikely to provide charge-level accuracies better than 25%.

The relative charge level, often called the state of charge (SOC), is defined as the ratio of residual charge to the battery's charge capacity. Hence charge flow must be measured and monitored through a procedure called "coulomb counting." In practice, coulomb counting is accomplished by integrating the currents flowing into and out of the cell. To measure these currents with a high-resolution ADC, one typically connects a small resistor in series with the anode."

Here is a datasheet I found for an Atmel AVR352 that you could use for coulomb counting:

Even better would be to refer here.

And there are devices.

Though as far as I can see there is plenty of info on the web; i don't see how you could have missed it.

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