Re: battery life

[Mich Lanners <mlan@cpu.lu>]

On  28 Apr, this message from Michael Schmitz echoed through cyberspace:
>> After studying some Li-ion battery docs, I found that
>> end-of-discharge voltage for those batteries should be 3.0V. I
>> noticed PMU still gave me 14.0V when charge was aproaching 0%; so I
>> decided to let it drain down to 12.0V (4 cells in series). That gave
>> me another 45 minutes of runtime.
> 
> Yep, that's what I noticed as well (in MacOS, not Linux). What's the
> voltage calibration? My battery starts at a reading of 11911 ...

I suppose, at least for my TiBook, that it's simply mV. That would match
the fully-charged/end-of-discharge voltages I see for my battery pack (4
graphite Li-ion cells in series) on the TiBook.

Are you sure you have the same battery technology? Your end-of-discharge
of just above 10V suggest that you may have Li-ion cells with coke
cathodes (older technology). On those, however, you should also reach
4.2V per cell when fully-charged, vs. 4.1V per cell on graphite.

> I gave in and ordered a replacement battery from a third party
> distributor. They must have bumped battery capacity in the Pismo
> models, max charge of the new one is 5400, that lasts about 3.5 hours.

It could be more recent battery technology. Did you know there's a
standard for smart batteries? There's a whole site about that:

	http://www.sbs-forum.org/

AFAIU, these batteries _always_ include the microprocessor controlling
the charging, and giving the capacity readings, inside the battery. That
makes sense... And it means PMU reset probably has no influence on
battery capacity.

> Weird things happen with both batteries installed: with AC connected,
> at least the big one is continously discharging a bit then recharging.

I wouldn't know for sure, but depending how both batteries are connected
together, weird things could happen... although I imagine Apple's
engineers be smart enough to couple both batteries via protection diodes
preventing the lower-voltage battery discharging the higher-voltage one
:-)

>> > I'll have to try that again now that battery life is degrading. Max
>> > charge of 1745 is OK for Lombard, right?
>>
>> Looks good to me... My TiBook is down to 1574 :-(
> 
> Repeat the 'deep' discharge a few more times and check again. Might be
> necessary to do a PMU reset even (I'm sure I had a PMU reset in the
> meantime)

I'll try again. Since with that capacity, I'm down to three hours anyway
(with low activity and backlight turned down...), even if the deep
discharge eats even more lifetime, that wouldn't change much.

>> What do other people get as voltage reading when their battery is
>> fully charged, and when aproaching 0% charge? I'd be interested to
>> see if PMU always stops discharging 'early', as it obviously did for
>> me (at 14.0V vs. end-of-discharge at 12.0V).
> 
> The old one starts at 11900, ends around 10530.

Hmmm, fully charged at 12V? That doesn't sound like Li-ion cells... That
could be 10 NiMH cells in series. But I may be wrong...

> Charge goes down to 6
> and time remaining to 15 sec. and this does slowly decrease for about
> five minutes before the machine shuts down the hard way. Final voltage
> reading: 10379, with charge at zero for 15 minutes before powerdown.

Yeah, in my experience final powerdown will be when the voltage reading
goes below the cutoff threshold.

Cheers

Michel

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