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borunov is offline borunov
2010-06-04 , 20:38
Posts: 2 | Thanked: 0 times | Joined on Jun 2010 @ Ekaterinburg, Russia
#1
Hello,
I'm using PR1.2 with kernel 2.6.28power37. After loading kernel module bq27x00_battery I get two different ways to get percentage of battery capacity.
the first is using BME:
Code:
Nokia-N900:/home/user# hal-device bme | grep percentage                                    
  battery.charge_level.percentage = 55  (0x37)  (int)
the second is using bq:
Code:
Nokia-N900:/home/user# hal-device computer_power_supply_battery_bq27200_0 | grep percentage
  battery.charge_level.percentage = 76  (0x4c)  (int)
that is at the same time on the same device!
the first set of questions is:
  • which value is correct (I believe second )
  • why system going down when BME's value is zero? why not bq's value?
  • may be BME and bq are conflicted? may be I must unload some part of BME and bind bq to somewhere? how?

Sometimes ago I purchase BL-5J GOLD battery. in front of it is placed 1930 mAh. but BME says me
Code:
Nokia-N900:/home/user# hal-device bme | grep reporting
  battery.reporting.design = 1248  (0x4e0)  (int)
  battery.reporting.last_full = 0  (0x0)  (int)
  battery.reporting.current = 602  (0x25a)  (int)
  battery.reporting.unit = 'mAh'  (string)
only 1248 mAh!
the second set of question is:
  • may be BME "don't know" that there is a new, bigger battery and disable more charging? where can I tune BME to allow it that?
  • or may be I'v got china fake from London ?
thanks for your answers
 
borunov is offline borunov
2010-06-05 , 18:27
Posts: 2 | Thanked: 0 times | Joined on Jun 2010 @ Ekaterinburg, Russia
#2
can somebody help me?
 
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Naranek is offline Naranek
2010-06-05 , 20:55
Posts: 236 | Thanked: 149 times | Joined on Jul 2007 @ Finland
#3
The battery level is measured from the battery voltage, but the voltage drop isn't linear. Measuring the level is not a precise art, and I suppose that the two programs measure the battery level in a different way.

From now on this post is just speculation based on my own observations:

At least in Maemo 4 the original Nokia battery indicator doesn't give you exact battery level. I believe this to be a conscious decision that's made because - as I said, you can't measure the level that precisely. Having compared the APM and Nokia's own indicator I've come to the conclusion, that BME shows high capacity longer and then drops suddenly. APM on the other hand seems to indicate the true level.

The system going down when BME's value is zero, but bq's not supports this theory. The batteries really don't like being drained completely, so shutting down the device early makes sure that the batteries don't die because if misuse.

I can only guess that the reason for this is to keep the user happy. If you know that "The device is OK until the battery indicator starts dropping, and then it will fail quite quickly" you'll use the device merrily until that point, and then use it only if you need to. With a constantly decreasing meter you'll be constantly worrying "now it's 72%... now it's 65%... how long will it last?"

About the fake batteries... the battery technology in use is pretty constant. For a certain technology and certain size you'll get certain capacity. If someone advertises a bigger capacity battery with the same size, it's most probably a fake. There's no way Nokia would use batteries that waste space if they could instead get longer talk time or smaller size & weight to the spec sheet.
 
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