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mike[_22_]

On 10/29/2012 2:26 PM, wrote:
On Sun, 28 Oct 2012 15:19:53 -0700, wrote:

It's a crap shoot.
Depends a lot on the technology and the vendor.
I've had zero luck with IBM. Once the "chip" shuts off, it's
all over.

What do you mean when you say "when the chip shuts off"?
Does the computer shut down when the battery gets too bad?

This is an IBM T-43 laptop.

Dells resort to an error condition, but the pack works.
Had one with a PIC processor...resetting the processor fixed it.
Others have no issues at all.
Got one that will charge, but the computer won't run on AC, it
defaults to battery. Only way to charge it is to leave it off.
Only way to run it on AC is to remove the battery.

Mine runs from the AC power cord just fine. I never tried it with the
battery removed.

You can buy software that claims to reset chips, but it costs
more than a new pack. And it requires some hardware.
Not clear if it's updated to the latest stuff.
I've never found resetting info on the web.

Please explain. Where is this chip and why does it fail?

snip

You can buy external batteries that plug in the ac adapter socket.
Not optimal, but they can work with different laptops.

I've seriously considered using an external battery such as a motorcycle
or garden tractor battery. They are small and light enough to carry
easily. 90% of the time I run this computer on AC or plug it into my
car's cigarette lighter. The internal battery only gives me about a
half hour these days, (even if I leave it plugged in all the time when
not in use), so it's becoming fairly useless. The meter says the
battery is only operating at 47% capacity. Considering that, a brand
new battery is only good for about an hour. I think an external battery
should last much longer, and can be charged with a common battery
charger too.

Are we having fun yet?

OK, the "chip" is a small computer that keeps track of the battery
and communicates with the laptop. Depending on the battery technology
and the particular chip, there can be a lot going on.

The particular task important here is battery voltage monitoring.
The chip tells the laptop what it thinks the remaining capacity is.
The laptop is responsible for making sure that the battery is not
overcharged or undercharged. But the battery chip also knows what
are safe voltage levels and can disconnect the battery independent
of the laptop's wishes.

When overdischarged, lithium cells are not only dead, they're unsafe.
They can catch fire if you try to recharge them. Vendors don't like
lawsuits, so they're very conservative about how low the cells
can discharge. At some point, the chip PERMANENTLY disconnects
the cells and there's nothing you can do externally to turn them
back on. If you replace the cells, the voltage goes to zero
and the chip latches off. New cells won't help, the chip is
still turned off. They won't tell you how to turn it on from
the internal bus.
You'll find youtube videos on how people added power supplies to
keep the chip powered while replacing the cells "hot".
Another problem is that even if the chip doesn't turn the system
off, it sometimes remembers the old battery capacity and reports
that to the laptop which turns off based on the wrong number.
It's always something.

I haven't tried replacing cells on anything newer than about 2006 vintage
laptops. The safeguards seem to be more stringent with time.

My experience is that the primary failure mode for a laptop battery
is increased internal resistance. I built a computer-controlled
battery test system and verified that, at low current, a "bad"
laptop battery can deliver almost all of it's rated electrons.
But the laptop is a High current pulsed load.

The sense voltage is depressed by the internal series resistance
and the voltage sense shuts the system down while there's still
lots of electrons left to be had.
That's compounded by the resistance raising the sense voltage
under charge, so the charger shuts off before delivering the
full number of electrons.

This could be fixed, but there are factors that prevent that.

1)customers want the smallest/lightest laptop possible. Bigger battery
is not an option. Vendors advertise battery life under optimum
conditions on day one. After that, you're on your own.

2)there's more profit in a replacement battery than there was in the
whole laptop. That's why you don't find a standard battery that
works in any laptop. That would make it a commodity and kill
the profit margin.

Do not underestimate the safety issues in rebuilding battery packs.
Back in the day of NiCd packs, I blew up one. If I hadn't been wearing
safety glasses, I'd be typing this on a braille keyboard.

There's no way you'll save money rebuilding one or three packs.
If you have time on your hands and a lot of equipment, it can
be a fun hobby, until you get bored.