Funny battery values (nx6325)

Joerg Wunsch j at
Wed Mar 17 16:18:37 UTC 2010

As Kevin Oberman wrote:

> FWIW, IBM/Lenovo recommend that, should the battery capacity stuff
> get messed up, you FULLY discharge the battery and then re-charge.

I'm doing that right now with my TP 600E battery, too.  It was
completely dead (one out of the three cell pairs had 0.0 V), so I
replaced all cells by some other 18650 cells I've got around.  While
the machine yelled "Battery critically low" after only about 5 minutes
of run-time, it already lasts for half an hour now.  I hope I'll also
be able to re-train the Coulomb meter chip in the battery there.

> This is claimed to re-initialize the values stored in the battery
> and I found this worked on a battery in my old 600E. Mine did not
> have a weird "Design Capacity" value, though.

Same here, the "Design capacity" of that TP 600E battery makes sense,
unlike on the nx6325.

As Ian Smith wrote:

>  > > Is this consistent or does it vary from boot to boot or if you
>  > > disconnect and reconnect the battery?

> Or try another battery?

Only got that one.  The machine is normally a semi-desktop one.

>  > That's right, but it wouldn't be supposed to affect the "Design
>  > capacity", would it? ;)

> It wouldn't be supposed to :)

> Tracing back through acpi_cmbat_get_total_battinfo in acpi_cmbat.c
> indicates that calculaing remaining time does uses last full
> capacity, but from there back through acpi_cmbat_get_bst and
> acpi_cmbat_get_bif it's all just retrieval, from acpi packages of
> _BST and _BIF

Thanks for the analysis!

> Most of it must be stored in the in-battery chip, but I don't know
> where specs may be, or even whether they all use same protocols.

I think this is all called the "Smart Battery specification", which is
essentially a layer on top of a standard I²C bus.  I once looked at it
lightly in connection with a battery control IC as I did build my own
battery (out of used 18650 cells, again) for a ham radio transceiver.
But I haven't really looked into the Smart Battery specs so far, as my
transceiver didn't want to talk it anyway. ;-)

> Peter's factor of 10 sounds plausible.

Except for the design capacity value.

> You can dump your ASL (see Handbook for instructions) and search for
> something like:

Thanks for that hint, I'll do it as soon as the machine is back here.

cheers, J"org               .-.-.   --... ...--   -.. .  DL8DTL                        NIC: JW11-RIPE
Never trust an operating system you don't have sources for. ;-)

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