Re: TP750 Battery

["John H. Kim" <jokim@MIT.EDU>]

On Mon, 29 Jul 1996, Robert Dewar wrote:

> If you are concerned about prolonging battery life, then you should not
> store the battery in your machine while you are using it (I am a little
> curious as to why you *do* store the battery in your machine if you
> know it is troublesome, and have already destroyed batteries this way).

You're looking at this with 20/20 hindsight, Robert.  Battery #1 died.
I chalked it up to age at the time.  Battery #2 died, and that's when
I began to suspect it was the charge cycle killing it (things were
fine until I started leaving my computer on all the time).  Since IBM
was replacing these things w/o question, I used battery #3 to test if
the charge cycle really was killing it.  I left it in for a little
over a month.  It died.  I called IBM, and the rep pointed out the
warranty was only 1 year.

Another reason to keep the battery in is as a UPS.  Not very important
if you're using DOS/Win, but very nice if you're running OS/2, Unix,
NT.

> Basically only Lithium-Ion batteries can be handled without worrying
> much about this sort of thing. Otherwise do NOT store a battery inside
> your machine if you want maximum life.

I have not been had any problems with leaving my 701's NiMH batteries
in all the time.  It's been there for over 5 months now, and still
runs the pad for about 3 hours.  The 701 does not do this 90% recharge
thing.  (Then again, the 701's batteries seem to hold their charge on
shelf much longer than the 750's batteries.) 

> So I don't see the 90% charge as destroying the battery, I see it as normal
> use -- i.e. what is necessary to keep the battery charged and ready to go
> at a moment's notice, which is what many users want.

If it's "normal" use, why does fully discharging it once a week help
extend the life?  (Battery #2 lasted about 3 months because I took
the machine on the road every week or two.  Battery #3 sat in the
750 for about 5 weeks without a full discharge, and promptly died.
--
John H. Kim       "I stop for red traffic lights" -- bumper sticker 
jokim@mit.edu     commissioned by the City of Boston as part of a
MIT Sea Grant     campaign to shed its reputation for bad drivers.