"Jeff Liebermann" wrote in message
...
On Sat, 12 Jul 2014 18:52:20 -0700 (PDT), Tim R
wrote:

So, what is it that kills laptop batteries?

Laptop batteries are LiIon and do not have anything to do with the
mythical NiCd memory effect. Three things will help kill LiIon
batteries:
1. Leaving them on 100% charge forever.
2. Running them into the nearly total discharge.
3. Heat.

The details:
http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries
http://www.mpoweruk.com/lithium_failures.htm

I've had to replace several on the kids's laptops.

Let me guess(tm). You left the charger plugged into the laptop 24x7?

If there's no memory effect, and much of the damage is caused by
overcharging, is that the problem with laptops?

It's almost impossible to overcharge a LiIon battery. There's plenty
of electronics between the charger and the cells to prevent that. It's
also fairly easy to tell if a LiIon battery has been overcharged. They
just roll over and die with a shorted cell in a few hours.

However, leaving the battery on 99.99999% of capacity forever is just
as bad, but takes longer to trash the cells. See the aformentioned
URL's.

Should I be
retrofitting a better wallwart to these?

No. You should be using the one that came with the laptops or an
equivalent replacement. Plugging in the wrong charger is more likely
to kill the laptop charging circuit than the battery.

However remote - there's a possibility the wrong charger could over volt the
charge cut off chip in the laptop.

That would lead to full on over charging, thermal runaway and venting with
flaming gas.