[ltp] One battery or two?

[Henrique de Moraes Holschuh]

On Wed, 01 Oct 2008, Tino Keitel wrote:
> On Wed, Oct 01, 2008 at 11:02:07 -0600, Christos Papadopoulos wrote:
> > I am facing an interesting dilemma.
> > 
> > I have both the regular (8-cell) and extended batteries for my X40.
> > Which is better for maximizing battery life, leaving the extended
> > battery plugged in, or not plugging it in?
> 
> In general, keeping the batteries always plugged in one of the worst
> things you can do with your batteries. They are exposed to heat, are
> constantly recharged and are therefore stressed a lot. You can do
> something against the recharge cycles using tp-smapi, see below.

And if you are going to keep them unplugged, leave them at ~40% at a
temperature in the 5°C to 15°C range, without frost.

> According to http://www.thinkwiki.org/wiki/Tp_smapi, the X40 supports
> setting the percentage at which the battery should be recharged. If you
> set it very low, the battery will be recharged less often.
> 
> I set it to 20% on my X61s. With the 8-cell battery, this gives me at
> least one hour of remaining battery time, while keeping the number of
> recharge cycles low.

Deep discharges are also bad.  I'd suggest never draining it below 30%
unless you do have to (hey, not using the battery when you'd need it is a
far worse error than using it incorrectly, as the thing will degrade with
time anyway :-) ).

> > but "strain" the regular battery more. If I plug it in, both batteries
> > may share the load and the recharge cycles (or does one discharge after
> > the other?).

The batteries never share the load.  They charge and discharge one at a
time, and the EC/BIOS is DOWNRIGHT EVIL about it at least up to the T43: it
will fully discharge whatever battery is active before switching to the next
one.

You *REALLY* need to use tp_smapi and some monitoring userspace thing if you
like to use two batteries in the T4x series (and R5x) if you don't want to
destroy your bay battery too soon (the BIOS prefers to deplete it first if
AC goes out when both batteries are installed).  I don't know how the X40 EC
behaves, it DOES have a slightly more advanced BIOS than the T4x, so the EC
could be less stupid as well...

> When I used 2 batteries in my A30, they were discharged one after
> another. With tp-smapi you should even be able to choose what battery
> is be discharged first.

You can select which one is to be discharged, yes.  Just be careful not to
leave the force_discharge setting enabled, because it DOES NOT GO AWAY when
you plug in the AC adapter!

-- 
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh