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Author Topic: Should I worry about how I treat the battery?  (Read 1201 times)
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I have an Arduino Fio with some no name 3.7V 1000mAh battery. As far as I know the battery came along with the Fio when ordered from SparkFun.

In a thread I started earlier about measuring battery lifetime (http://arduino.cc/forum/index.php/topic,105546.0.html) a user comments about abusing the battery "You are trying to beat a battery to death, making it do various things, measuring how long those various things take to kill the battery. That's what I meant by abuse."

I expected that either the battery itself or the Arduino has a simple Battery Management System of some kind that protects from both overcharging, does it not?

I also thought that for lithium ion batteries, there is no other treatment than overcharging that can harm the battery. Of course any kind of normal use will wear the battery a little. Am I wrong?

Velle
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Quote
I also thought that for lithium ion batteries, there is no other treatment than overcharging that can harm the battery

There is at least a couple of treatments that will destroy a LiPo

If you discarge it under 3 Volt it might die
If you charge it with to high current (typically you use 1C)
If you draw too high current (it might explode)
If it is a typical LiPo used in RC models, there is absolutely no protection circuit, as the one ones from fx. cellphones
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Are we talking Lithium Ion or LiPo (lithium polymer) here?  LiPo are much more dangerous (do not charge unattended, watch out for swelling, always use a protection circuit (some have them built-in, BTW, but its hard to be sure without dissection).  Lithium Ion are more stable in the longterm but still its a lithium battery.  The safest are LiFePO4 lithium ion cells which are harder to set alight.

So the answer to the subject line is "yes".
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Thanks.

I've found out that it is a lithium polymer battery. It looks very cheap and simple, so I didn't expect the battery itself would have any protection. Being the curious and irresponsible I of course started 'dissecting' it. I think/thought that there would be a few cells inside, so I just wanted to remove the foil to see the cells. But it wasn't easy to remove at all. And in the process of trying to cut through, I cut too far. Sparkles, hizzes, and a bad smell of glue and fire resulted. I'm just going to conclude that it does not have any circuitry, thus no protection. It would have to be incredibly compact to fit in there. The left battery if for reference, the right shows where I cut through.



The Arduino has a 'charge' lamp, that turns off at some point, so I trust that it does protect from overcharging.

Wouldn't it be irresponsible if it did not also protect from draining the battery below the healthy limit? However, in this post they write "does not appear" to protect from over-discharging.

That would mean that in any use case of Arduino Fio, no matter how simple/complex, the application design team needs to implement their own protection. Unless they want to be irresponsible as well, of course. It really seems stupid and wrong, doesn't it?

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The Arduino does not have a charge circuit. I don't know what you mean by "charge light." Could you describe it, or post a photo?

Those cells are the raw chemistry. Two electrodes, and the Lithium electrolyte, wrapped together in a foil package. It's hard to tell whether the cell is cheap or expensive, because that's how they're made -- what you're seeing is what's on the inside of a cell phone battery that in turn is wrapped in harder plastic, and typically some protection circuitry (although some devices put the protection in the device, not the battery.)

It's more common to see the protection circuitry in form factors that allow for some slop, such as round cells (18650 size, for example.)

Also, charging LiPo cells is not like charging lead-acid batteries, or even NiCd cells. LiPo want a constant current charge of about 1C (e g 1 Amp for a 1000 mHa cell) until it reaches a threshold voltage (say, 4.15 V) and then a constant-voltage charge (say, 4.15 V) until the current falls below some lower cut-off (say, 100 mA,) and then it wants you to stop. This will ensure the longest lifetime of the battery. Most chargers will do something like this for you. Protection cells do not -- they just make sure to cut off charging if you go above the recommended max -- typically, at 4.2V.
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You write that Arduino does not have a charge circuit.

While charging:


When battery is fully charged, and USB cable still plugged in:


If I then unplug and replug the usb cable it will start charging again, but only for a minute or so. I'm pretty sure that it has to be a protection against over-charging. The text on the yellow diode is "CHG".

Furthermore I found some schematics of the Fio board. I have attached a section that has smth to do with the battery, even though I am not able to understand it:


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I missed the "Fio" part :-) Yes, the Max1555 is a fine LiPo charging control circut for small LiPo cells. Note that it charges at most a single cell, at 280 mA (100 mA when using USB power.) If all your battery management goes through that circuit, then the main things you need to worry about are puncture/mechanical stress on the cell, and perhaps over-temperature if the battery temperature doesn't make it back to the charger.

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