[Leica] Bad luck with Hong Kong battery

[lrzeitlin at gmail.com (Lawrence Zeitlin)]

Herbert Kanner writes of his disappointment with a Hong Kong li-ion battery.
I'm not surprised. We used to use a variety of li-ion batteries made by
different manufacturers in laboratory equipment and many differed in
characteristics. The li-ion battery is a relatively new battery technology,
dating from the 1970s. Manufactures use a variety of anode and cathode
materials in these batteries, containing lithium, of course. The self
discharge is lower than the 30 to 35% per month expected of nickel metal
hydride batteries but they do self discharge, normally 10% per month.
Multiple cell batteries have a built in electronic circuit which equalizes
charge and discharge of the cells. These self discharge faster because of
the circuit drain. Relatively few manufacturers make the actual battery
cells although many different companies package them to suit individual
requirements. Leica certainly doesn't make the batteries which it supplies.
The trick is to find the company that makes the actual cells and buy after
market or third party batteries which contain those cells. Perhaps someone
on the LUG knows.
Here is an excerpt from Wikipedia containing self discharge information on
li-ion batteries.

Prolonging battery pack life

? Depletion below the low-voltage threshold (2.4 to 2.8 V/cell, depending on
chemistry) results in a dead battery which does not even appear to charge
because the protection circuit (a type of electronic fuse) disables it. This
can be reversed in many modern batteries, especially single-cell ones, by
applying a charging voltage for long enough to make the cell voltage rise
above the low-voltage threshold; however this behaviour varies by
manufacturer.

? Lithium-ion batteries should be kept cool; they may be stored in a
refrigerator.

? The rate of degradation of Lithium-ion batteries is strongly
temperature-dependent; they degrade much faster if stored or used at higher
temperatures.

Multicell devices

Li-ion batteries require a Battery Management System to prevent operation
outside each cell's Safe Operating Area (over-charge, under-charge, safe
temperature range) and to balance cells to eliminate SOC mismatches,
significantly improving battery efficiency and increasing overall capacity.
As the number of cells and load currents increase, the potential for
mismatch also increases.[87] There are two kinds of mismatch in the pack:
state-of-charge (SOC) and capacity/energy ("C/E") mismatch. Though SOC is
more common, each problem limits pack capacity (mA?h) to the capacity of the
weakest cell.


Larry Z