Document with answers to most popular battery-related questions is ready

Wolfgang Spraul wolfgang at
Sun Aug 2 19:46:26 CEST 2009

Paul & Joerg,
this is an excellent document, obviously I cannot spot anything wrong!
I didn't know that some external chargers would not charge gta01 or gta02
batteries because of the thermistor check you are writing about.
All the cheap external chargers we bought in Taiwan or China for testing can
charge both gta01 or gta02 batteries without a problem.

I have a question for all:
We will ship our first NanoNote with a BL-4C compatible battery, without
Coulomb counter (middle pin unused) [1].

How are people really using the Coulomb counter in gta02?
Theoretically I would think that it provides far superior power measurement
options for actual software development, just as you write.
For example when playing with power saving codes, whether in the kernel,
middleware or applications, I would think over the course of several hours or
days the Coulomb counter data is the primary means for efficient development.

So we are considering shipping the next version of the NanoNote with Coulomb
counter batteries same as the Neo FreeRunner.
But if nobody is actually using the data from the Coulomb counter, then it's a
wasted effort.

What do you think?
Was the addition of the Coulomb counter in gta02 really a useful thing?
Did FSO developers or kernel developers use the data for power optimizations?



On Sun, Aug 02, 2009 at 09:07:39PM +0400, Paul Fertser wrote:
> Hi,
> This is a text version of the wikipage [1], feel free to ask new questions
> there on the talk page. Discussion on this ML is also appreciated (and
> in fact i'm more comfortable with ML than the wiki).
> Openmoko devices
> Battery questions and answers
> NB: Some of the described behaviour depends on the kernel, the
> relevant code was pushed on 02 Aug to andy-tracking
> Hardware capabilities
> Q: What batteries can be used with gta01 and gta02?
> A: Original OM gta01, gta02, Nokia BL-5C, BL-6C and compatibles.
> Q: Do other BL-5/6C compatible batteries fit?
> A: If the battery is thicker than BL-6C, you won't be able to close
> the back cover.
> Q: What is the difference between all those types?
> A: 
> Capacity:
> gta01, gta02		- 1200 mAh
> BL-5C old (newer/new)	- 850 (970/1050) mAh
> BL-6C			- 1150 mAh
> Temperature control:
> gta01, BL-5C, BL-6C	- thermistor
> gta02			- bq27000
> Special features:
> gta02 - accurate and sophisticated reporting of capacity,
> time_to_full, time_to_empty, temperature and battery current during
> both charge and discharge thanks to bq27000 (aka Coloumb Counter)
> Q: What are hardware capabilities of gta01 and gta02 with regard to
> battery management?
> A:
> gta01: charging all battery types, measuring temperature with
> battery-integrated thermistor (currently charging and measuring
> temperature for non-gta01 batteries doesn't work due to the kernel
> driver issues but it's software limitation), measuring battery output
> voltage, very inaccurate and noisy measuring of battery current
> gta02: charging all battery types, measuring battery output voltage,
> communicating with bq27000
> Q: Can nokia phones use/charge gta01/gta02 batteries?
> A: gta01 and gta02 batteries will fit wherever BL-6C fits but they
> can't be charged in nokia phones unless you isolate the middle pin
> from the battery and connect a resistor of ~50k (actual measured value
> on a cold (25C) battery is 75k, on a slightly warm battery - 82k) from
> it to the ground (to fake a thermistor presence).
> Q: Can third-party chargers charge gta01/gta02 batteries?
> A: The "good" ones will most probably require the same trick needed
> for nokia phones. More cheaper ones are more likely to ignore
> thermistor absence. 
> Q: I have several compatible batteries. What are the storage
> requirements for them?
> A: Keep in a dry cool place charged to no more than 75%.
> Safety issues
> Q: Do OM devices control temperature to stop charging if the battery
> gets too hot?
> A: No (probably gta01 does, need to check).
> Q: Isn't it dangerous?
> A: No, since all batteries (not raw cells!) have an integrated
> protection circuits.
> Q: Can i use that fancy 2800 mAh BL-5C-compatible battery i saw on
> ebay?
> A: Unless you want an explosion in your pocket i wouldn't recommend
> using any battery that is not produced by a reputable vendor and
> widely tested. And even reputable vendors make mistakes, nokia once
> had to recall 46 million batteries manufactured by Matsushita (
> ).
> Q: You say that BL-5C is compatible with my gta02. Does that mean i
> can use that BL-5C-compatible bat i bought for a buck from a bum?
> A: You bet, go ahead.
> Charging
> Q: My battery charges to 100% but then charging stops and the battery
> keeps discharging, wtf?
> A: LiIon batteries don't like to be kept fully charged, so the charger
> stops as soon as charging current becomes less than threshold. If you
> have GSM on it will discharge the battery.
> Q: But why doesn't it ever stop charging on my device?
> A: The GSM modem is connected directly to the battery terminals so if
> it's active, charger will think it's still charging the battery and
> won't turn off unless GSM becomes inactive. The default threshold is
> about 16mA, the latest Qi increases the threshold to ~32mA.
> Q: Does it mean if i leave my phone plugged it will eventually fully
> discharge the battery?
> A: On gta02 the charger will restart the charge automatically once the
> battery voltage reaches ~4V which corresponds to ~76%. Not sure about
> gta01, requires more investigation. :-/
> Q: Ok, how to make sure my battery is fully charged before a long
> trip?
> A: Replug the charger, it will trigger charging no matter what the
> current capacity is.
> Q: My power/aux LED indicates charging/discharging/whatever, what does
> that mean (aka why it's still blue even after i unplugged the
> charger)?
> A: Ask FSO guys about it, some of them think that the user shouldn't
> really know what's happening and therefore they do some special
> mangling of "status" sysfs node before presenting it to the user. If
> you want to make a decent bugreport please add clear steps to
> reproduce and /sys/class/power_supply/battery/uevent contents for all
> relevant states.
> Using compatible batteries with gta02
> Q: So, how do i use "dumb" batteries with my freerunner?
> A:
> First you need to unbind bq27000 driver:
> echo bq27000-battery.0 > /sys/bus/platform/drivers/bq27000-battery/unbind
> Then you load the dumb battery driver:
> modprobe gta01_battery
> If you need to use bq27000 driver again, do:
> rmmod gta01_battery
> echo bq27000-battery.0 > /sys/bus/platform/drivers/bq27000-battery/bind
> If you use Enlightment you might need to restart it after that.
> Q: Is capacity reported for dumb batteries accurate?
> A: During discharge it should be pretty (+-10%) accurate, during
> charge the capacity reported is ~20% more than real.
> Q: Why does /sys/class/power_supply/battery/charge_full says i have a
> 850 mAh battery no matter what i use?
> A: It's a workaround to make popular battery gadgets work with this
> driver.
> This Q&A were prepared by
> Paul Fertser <fercerpav at>
> Joerg Reisenweber <joerg at>
> [1]
> -- 
> Be free, use free ( software!
> mailto:fercerpav at
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