Subject: Re: Battery info (Re: ACPI userland issues)
To: Garrett D'Amore <>
From: David Laight <>
List: current-users
Date: 06/21/2006 20:23:53
On Tue, Jun 20, 2006 at 03:09:12PM -0700, Garrett D'Amore wrote:
> The battery controllers I've worked with have "design capacity", and
> "maximum capacity", where maximum capacity is determined by the on-board
> micro.  I'm not sure exactly how they track the maximum, but I believe
> it is pretty much the "last full charge".

The controller I know about (BQ2050??) resets its view of battery capacity
if you do a discharge from 'fully charged' to below the low voltage
threshold in one pass.  There are some gotchas though:

- you may have to write one of the battery gauge registers in order
  to get above the existing 'fully charged' point.

- every time you change from charging to discharging (and vv) the bottom
  8 bits of the 16 bit charge counter get zeroed.  This causes the
  gauge to misread badly.

- if your OS decides that the battery is discharged by using information
  from the gauge (rather than the battery voltage warning levels) then
  you will never resynchronise the gauge at all.

ISTR some experiments that showed that Lion batteries tended to fail to
take up charge as easily when they got older - and that the actual
capacity reduction was relatively slow.


David Laight: