mm wrote:
I've read a lot here about replacing the batteries in rechargeable
battery packs, but always about portable power tools.

Is it also possible to do this with battery packs for laptop
computers?


A friend was given a beautiful, used laptop, but doesn't have enough
money to buy a brand new battery. Can individual cells be replaced at
lower cost?

The answer to your question is obviously YES.

But, if you add the additional requirement that it not catch
fire, the answer turns to NO.

You can replace ALL the cells in the pack. About all you need is a
source for the individual cells and a tab spot welder.
The cells are hard to buy, cause they don't want to be liable
for you catching fire.
Since most people don't have a battery tab spot welder, they solder
on the cells, damaging them and increasing the risk of fire.

Yes, you can buy tabbed cells you can solder on. But they're
packed so tightly that the thickness of two tabs and the solder
joint won't fit back in the plastic.

And when you do find them, the total cost is about what a pack would cost.
You won't find them at OEM prices unless you buy OEM quantities.

Then there's the problem of resetting the battery monitor chip.
Older units reset themselves. Newer ones require some fixture
to reprogram the chip.
There's a company that sells a chunk of software and gives
you plans to build the interface. Problem is that it doesn't do
every battery. And the software is more expensive than a new battery.

Carefully weigh the potential cost savings against the cost of
replacing your house...assuming you're insured for stupidity...
or the cost of an eye if it blows up while you're working on it.

Remember, when the lawyers for the estate of your friend sue you,
your insurance probably won't help much.

NEVER, EVER, EVER REBUILD A BATTERY PACK FOR SOMEONE ELSE.
NEVER SELL A SYSTEM WITH A BATTERY YOU'VE HACKED ON.
NO GOOD DEED GOES UNPUNISHED.