On Sun, 24 Apr 2016 22:29:34 -0700 (PDT), Phil Allison
wrote:

** The charges that really "suck" are ones that ruin
the cells in short order by overcharging and hence
overheating them. Ones that rely on sensing the temp
of a cell or run for a fixed time are the main offenders.

The temperature sensing chargers are the worst. I used to deal with
them in Kenwood handheld radios. There was a translucent red window
in the bottom of the radio battery pack and another in the base of the
drop in charger. When the NiCd battery got hot, the IR radiation
would go through the windows to a sensor of some sorts in the charger
and turn off the charging. At least that was the theory.

The problem was that by the time the surface of the NiCd battery cells
were hot enough to register a temperature increase, it was already too
late. For NiCd chemistry, the battery only gets hot AFTER it
overheats. This system was really good for killing battery packs.

However, there was another problem. When the charger recognized that
the battery was hot, it would shut down. After a while, it would cool
down, start charging, and repeat the cycle over and over until the
battery was finally truly and totally dead.

When NiMH arrived, things changed for the worse. Using a temperature
sensor wouldn't work because NiMH normally would get warm while
charging. Instead, there was a tiny drop in voltage just before the
battery reached full charge. The smart charger chip would detect this
drop in voltage and declare the battery to have been successfully
charged. That works well until you drop a fully charged battery into
the charger. There's no drop in voltage and the charger just keeps
charging until the battery overheats and is truly dead.

LiIon chargers are all smart and do a good job of preventing
overcharging. You can create a problem with dirty battery contacts,
but that's rare. However, LiIon cells deteriorate when left at full
charge for too long:
http://www.mpoweruk.com/lithium_failures.htm
Same with leaving it discharged or too hot. The main culprits are
desktop replacement laptops, which tend to be left on charge 24x7.
Many newer laptop have a charge control that stops charging at 50 to
60% to extend battery life.
http://www.apple.com/batteries/maximizing-performance/
http://www.howtogeek.com/169669/debunking-battery-life-myths-for-mobile-phones-tablets-and-laptops/
The next generation of LiIon chargers just might have an adjustable
EoC (end of charge) control.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558