Certainly makes sense (get it?), doesn't it. Nearly every EVO owner I know has, at some point or another, complained about the fact that their battery life drops about 5-10% as soon as they unplug it. Well, it turns out that's because of there's an overcharge protection chip inside Li-Ion batteries.


XDA user willy900wonka decided to tear his extended EVO battery apart, and lo and behold:

What I found was that a 8205 chip is used to provide protection and prevent over charging and over-discharging. Here is a quote from a google search.

S-8205A/B Series Applications-Optimized-Battery-Protection Circuits.
All contained voltage detectors are of high precision between 15mV and 100mV depending on the function. Overcharge detection voltage is 3.55V..4.4V with 25mV accuracy. Overdischarge detection voltage is 2.0V..3.2V with 80mV accuracy. Discharge overcurrent detection voltage is 0.05V..0.3V with 15mV accuracy and charge overcurrent detection voltage is -0.05V..-0.3V with 30mV accuracy. The detection voltage in short circuit case is 0.5V..1.0V with 100mV accuracy.



So there you have it. Despite what some have said, custom kernels can't really defeat the protection... buzzkill. Better than burning out your battery though, I suppose.

[Source: XDA-Developers]

Aaron Gingrich
Aaron is a geek who has always had a passion for technology. When not working or writing, he can be found spending time with his family, playing a game, or watching a movie.

  • Darius_bd

    Dont all li-on bateries have overcharging protection embedded in it? And that's the reason why you can keep it plugged without problem while this aint true for (very) old nickel-cad batteries?

  • Robin

    I think that 5-10% thing is just a bug (at least on the HTC Desire).
    Use a battery monitor app and you'll see that it discharges every ~2hours up to 10%.
    I guess it's still running on battery even if it's connected to the charger. Due to android not entering deep sleep (edit: while charger is connected), it drains about 10% in 2 hours.
    I've read in a german desire forum that the latest firmware fixed that issue - I can't verify as I'm on T-Mobile (yeah, fragmentation...)

    • Tim

      Not sure which firmware you refer to but I've recently flashed LeeDroid 2.3d and noticed battery life on my Desire has improved considerably. Getting nearly two days if light use out of a single charge.

  • David Alderman

    AFAIK, virtually all Li-Ion batteries have integrated protection circuitry. The consequences of damaging a Li-Ion battery are rather dire so great pains are taken to make sure that does not happen.

    • Aaron Gingrich

      Thanks, updated the post a bit to say Li-Ion rather than EVO. Thanks! :)

  • A. Diaz

    Maybe this'll help. I bought two 3500mAh batteries from http://www.Seidio.com for my EVO and I believe they use Japanese lithium-ion cells and they instruct everyone to charge their phones at least 2 to 3 hours AFTER it reaches 100% full charge according to whatever battery app you're using. It works for the original battery that came with my EVO as well. Hopefully, this'll help others suffering this problem.

  • http://iandouglas.com Ian Douglas

    Excuse my ignorance, but does the overcharge protection mean we can just leave our devices plugged in all the time? (being careful about overheating, of course)

    • http://www.teamviewer.com/download/index.aspx Peter

      Yes, and the same goes for laptops.

      And you have to worry about overheating either.

      The charger ICs in li-ion batteries also have overheat protection where they monitor the cell temperature.

      The SII (Seiko Instruments Inc) S-8205A/B series charger IC use a PTC (Positive Temperature Coefficient) resistors to measure the cell temperature threshold and stops charging if the cells reaches the threshold temeprature.

  • Dano

    Yes, you can leave your phone plugged in whenever a charging source is available. Only during charging does it actually get hot. After charge it runs cool.

  • Wlly900wonka

    Thanks. The idea is that certain kernels, which trickle charge the battery and give much increased battery life as a result, are safe.
    The final charge control is incorporated into the battery. Using SBC from xda ms79723, I'm at 100% battery for 3 hours of light use.

  • Willis

    You are seriously quoting a press release to tell you the functionality of the protection IC?

    • Aaron Gingrich

      Actually, I'm quoting the guy who found the chip and looked it up.

      I know, I should totally have chip numbers memorized, so that I can mentally call them up at a moments notice!

  • http://batteryboss.org Doug Simmons

    In addition to overcharge protection they also have a low-end cutoff of, if I recall something like 2.7V.

    If you want to see a more intriguing picture than the shots on this article though, you should check this out: http://mobilitydigest.com/whats-wrong-with-this-picture/

  • joshua

    Go on eBay for the people that have a problem with the battery problem I purchased 3 batteries and a battery charger for 12 bucks now I have no problem ever!

  • JAMartinez1797

    pardon me but, what would I do when my phone overcharged? its almost a 12 hours of charge. i turned off my phone whenever I charged so out of that 12-hour, in 3 hours my phone already is full but i ddnt manage to plugged out. so it reaches 12 hours before i realize its overcharged already. :(