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NiCad cell voltage and amount of charge contained.

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treez

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If a Nicad cell is not being charged, and its cell voltage is measured as 1.54V or higher, then can one safely say that this cell is gauranteed to be at least 80% charged?
 

I have noticed that NiCads tend to have higher no-load voltages as they age or are consistently overcharged. I wouldn't take the no load voltage as an exact indication of the charge level. If you load the cell for some time, the voltage could drop considerably and recover slowly once the load is withdrawn. Individual cells could have different characteristics. I would assume that if measured and plotted the individual cell's voltage/charge, that could be used to predict the charge for a given voltage(for that individual cell). Then again, my experience has been that this changes with cell aging.
 
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A Ni-Cad cell might be 1.5V when it is fresh out of the charger then the voltage slowly drops to about 1.25V.
I have some Ni-Cads that were fully charged a few days ago and most measure 1.28V today.

I charged some Ni-MH cells to 1.5V a week ago and today they measure 1.35V.
 
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80% it`s cool. NiCa IMHO it is good chemistry but not friendly with nature. Typically it alive 500-1500 cycles with capacity degradation 50%. First problem is internal resistance increasing ( degradation ) with cycles . By my experience it should be bellow 0.1 Ohm for 1A/h cells and for 10A/h- 0.01 Ohm respectively. It happens with fast charge above 0.5C and without normal discharge- charge cycles. Partly battery atrophy.
 
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