[Tfug] Li-on battery

[John Karns]

On Wed, Feb 20, 2008 at 8:10 AM, Jeremy D Rogers
<jdrogers at optics.arizona.edu> wrote:
>
>
> In my experience, deep cycle = badness. I'm no expert, but I think a lot of
> the deep-cycle advice out there is carry over from other chemistries like
> NiMH that suffered 'memory effect' that would get reset by a deep cycle.

Yes, as another responder mentioned, the Ni-Cads were the ones that
suffered from memory effect.  But in any case, I've had other laptops
with Li-Ion batteries inadvertantly run until the battery was depleted
(although I attempted to set auto-shutdown limits for ACPI / APM, it
never seemed to actually work) without suffering loss of the battery.


> Unfortunately, this doesn't really work on Li-ion. The only thing like that
> for Li-ion is resetting the internal calibration that tries to know what %
> you have left. If you run it down, that gets reset and is more accurate, but
> this does nothing to the actual battery, so I just avoid that. From what I

My suspicion is that the problem is more attributable to the logic in
the pack than the cells, especially since it was exhibiting the same
characteristic of entering a state of not accepting a charge until I
powered of and momentarily disconnected the AC.


> read, Li-ion dislikes deep cycles, and if you go too low using something
> that is not acpi aware like memtest, it might really take a blow to the
> chemistry. The other thing is that Li-ion has a finite number of cycle
> counts (usually in the neighborhood of 300-400), and these cycles tick away
> even if the cycle is only from 100%-90% and back. That's why leaving the

>From my experience with other laptops, some with 5 or 6 year old batt
packs, it seemed to me that the charge had to get quite low for the
logic to increment the cycle count, but that's just casual
observation.


> battery in while on AC often wears a battery down even if you don't run on
> battery all the time. Some thinkpads win here, because (at least with my
> t60) you can set the charge thresholds so it won't start charging until it
> gets below 40% and stops charging at 70%. If I run on AC most of the time, I
> only use up only about one cycle every 2-3 weeks.
>  http://www.thinkwiki.org/wiki/Tp_smapi



> Which reminds me.. you can tell a lot about your battery on a thinkpad (even
> without tp_smapi installed) using "cat /proc/acpi/battery/BAT0/info" and
> also about the status using "cat /proc/acpi/battery/BAT0/state". That might
> help you determine what is going on.

Good idea.  I did look there, but nothing seemed to provide a clue.
When I checked it, it did seem to have a very small reserve left, so
it wasn't flat at zero.


> Sorry, I don't know about freezing and some of the other 'recovery'
> techniques out there, but I do know I lost one battery dead by draining it
> all the way (possibly even more than you did with memtest).
>
> Good luck,

Thanks for your response.

-- 
John