NiMH, NiCd battery nominal voltage and charged voltage

[Joaquin Bonilla]

I have a question regarding ten cells of 1.2 V single cell nominal
voltage
NiMH and NiCd.

I have just NiMH batteries available. I know that the NiMH cells have
not
very good self-discharge rate.

After a complete battery charge the measured voltage become 14.4 V. In
a
couple of days or so, the voltage dropped down to 12.6 V decreasing
the
self-discharge rate notably. It made looks like a pseudo "steady
state" the
battery voltage.

I ignore physical details about NiMH to understand this peculiar
transition
on voltages. I could make a guess although I would like to understand
the
real reason.

I consider that the cells after the charge were forced to a voltage
higher than
the nominal. Then the cells use a higher than the "regular" self
discharge rate up to the reach its nominal voltage. At that point the
discharge rate would decrease to become "nominal" too.

Has anybody an answer about this voltage transition? Would be similar
for
NiCd cells?

Thank you in advance,

JB

 

[CWatters]

Has anybody an answer about this voltage transition? Would be similar
for > NiCd cells?

NiMH discharge curve here...

http://www.thomas-distributing.com/techfacts3.htm

The voltage just after charging can be 1.5 V per cell

Nominal voltage is around 1.2 V per cell under 1C discharge but can fall to
0.9 V or lower under higher loads.