"Daryl" wrote in message
...

It sounds like they are being overcharged. That is prevented by a
simple card addition that prevents it on only of overcharging but
undercharging. Easy fix.

Daryl

The Lithium medical and electric vehicle packs I worked on were
controlled by ICs that monitored and recorded individual cell voltage
and overall charge and discharge current. Those are point measurements
that are easy to do. What's harder is detecting unexpected hot spots
away from the temperature sensors. Minor differences (improvements)
between the acceptance sample and production devices can change heat
flow paths.
http://www.mpoweruk.com/lithium_failures.htm