Funny battery values (nx6325)

[Kevin Oberman]

> Date: Thu, 18 Mar 2010 01:05:47 +1100 (EST)
> From: Ian Smith <smithi at nimnet.asn.au>
> Sender: owner-freebsd-acpi at freebsd.org
> 
> On Wed, 17 Mar 2010, Joerg Wunsch wrote:
>  > As Peter Jeremy wrote:
>  > 
>  > > >Design capacity:        279 mAh
>  > > >Last full capacity:     279 mAh
>  > 
>  > > Is this consistent or does it vary from boot to boot or if you
>  > > disconnect and reconnect the battery?
> 
> Or try another battery?
> 
>  > Currently, my wife is on a business trip with that machine.
>  > Hopefully, I'll also get a statement about how long it lasts on
>  > battery once she is back ;-), and I'll re-check those values then.
>  > 
>  > > >The battery is declared as 55 Wh, which would correspond to 5.1 Ah
>  > > >(probably 3 x 2 x 18650 cells).
>  > > 
>  > > But is also over 3 years old.  Almost everything you do to LiION
>  > > batteries makes their capacity drop.
> 
> Except keeping spares in the fridge, but not the freezer.
> 
>  > That's right, but it wouldn't be supposed to affect the "Design
>  > capacity", would it? ;)
> 
> It wouldn't be supposed to :)  caveat: I've only 5.5 sources to hand.
> acpiconf -i does no calculations, just prints what's given by
> 
>         if (ioctl(acpifd, ACPIIO_CMBAT_GET_BIF, &battio) == -1)
>                 err(EX_IOERR, "get battery info (%d) failed", num);
>         printf("Battery %d information\n", num);
>         if (battio.bif.units == 0)
>                 pwr_units = "mWh";
>         else
>                 pwr_units = "mAh";
> 
> etc, also answering mWh vs mAh display question.  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 .. presumably updated somehow via the EC, 
> but I'm in way over my head already ..
> 
>  > Can anybody tell where these values actually come from?  I could
>  > perhaps even build a small microcontroller gadget, in order to query
>  > the battery for its values offline (using I²C aka SMbus) in order to
>  > see where the mistake might be.
> 
> 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.  Sounds like 
> some fun, snooping EC <-> battery chatter and reverse engineering that - 
> assuming it occurs on an accessible smbus? - but maybe there's something 
> in the ASL that might be bent?  Peter's factor of 10 sounds plausible.
> 
> I'm interested in this because my T23 battery is just about dead, only 
> sometimes taking a charge now - that or the charging circuit is dodgy, 
> which I'll find out when the new battery arrives.
> 
> cheers, Ian

FWIW, IBM/Lenovo recommend that, should the battery capacity stuff get
messed up, you FULLY discharge the battery and then re-charge. They say
to turn off all automatic shutdowns so the battery will completely
drain. (This does mean an fsck on re-boot and I suggest that you do a
sync(8) when it gets close and, of course, don't have anything open.

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.
-- 
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at es.net			Phone: +1 510 486-8634
Key fingerprint:059B 2DDF 031C 9BA3 14A4  EADA 927D EBB3 987B 3751