RE: z50 battery oddity

[Khoa Tran <piper_the%hotmail.com@localhost>]

There are actually no such things as AA Li-Ion batteries, as far as the 
definition of AA is concerned (the "lithium AA" cells one finds in stores are 
non-rechargeable, and are entirely different from li-ion cells). Due to the 
chemistry involved, Li-Ion cells are 3.7 V. Alkalines come in at around 1.5 V, 
and NiMH and NiCad come in at 1.2 V nominally. The battery pack on the z50 is 
rated at 11.1 V, meaning that there are three Li-Ion cells in series (or six in 
series-pairs). The AA battery pack for the z50 would give you 12 V if you had 
Alkalines, but only 9.6 V for NiMH/NiCad. The discharge curves for these types 
of batteries are also different, meaning that the warning thresholds for Li-ion 
might be meaningless to the other battery types (hence my ongoing attempts to 
recalibrate the battery table for NiMHs).

The kicker, actually, though, is that li-ions are notoriously hazardous to work 
with. They're extremely finicky about charging, and there has to be a mechanism 
in place in the form of a charge control circuit to make sure that the cells 
don't vent/explode/otherwise cause unhappiness. What I don't know, however, is 
whether the charge control circuit is in the battery itself or if it's in the 
z50. In any case, the long and the short of it is that yes, you can replace the 
Li-ion cells, but the cells aren't readily available to consumers (I have seen 
them online and in surplus stores), and you run the risk of causing a toxic 
metal fire if you screw things up :P

Hope this explains a few things!


~k

> Date: Mon, 31 Mar 2008 11:18:48 -0500
> From: elijahr%gmail.com@localhost
> To: piper_the%hotmail.com@localhost
> Subject: Re: z50 battery oddity
> CC: port-hpcmips%netbsd.org@localhost
>
> On Mon, Mar 31, 2008 at 10:52 AM, Khoa Tran  wrote:
>>
>> Interesting thought! But the z50 batteries are definitely li-ion, 
>> unfortunately.
>>
>
> I know very little about rechargeable batteries. Would the z50 using
> li-ion cells make a difference?
> If there were indeed AA li-ions in the battery pack, why couldn't they
> be swapped out for something like NiMH batteries? I am under the
> impression that AA batteries have a standard voltage and amperage so
> are modular, though based in your comments, I am starting to feel that
> this is not the case.
>
> Additionally, it seems that many laptop batteries are repackaged
> li-ion AA batteries: see http://lowendmac.com/musings/06/0908.html
> So, couldn't one just swap for some higher quality li-ions, if the
> type of rechargeable battery does indeed matter?
>
> Cheers,
> Elijah Rutschman

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