NiMH, NiCd battery nominal voltage and charged voltage

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,


Reply to
Joaquin Bonilla
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As far as i know, almost all cells (primary and secondary) exhibit this initial higher-than-nominal condition. Mercury cells and Lithium cells appear to not have that pecular attribute.

Reply to
Robert Baer

NiMH discharge curve here...

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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.
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