How to tell if a cell is NiCd or NiMh?

Thread Starter

AlbertHall

Joined Jun 4, 2014
11,231
I have two unmarked cells, circa 1.2V terminal voltage.
How can I tell which chemistry they are, and hence which charger to use?
 

Audioguru again

Joined Oct 21, 2019
3,004
If the cells are the same size, a Ni-MH has 2x or 3x the capacity of a Ni-Cad.
While charging but before being fully charged, a Ni-Cad gets a little cooler but a Ni-MH gets a little warmer.
 

Audioguru again

Joined Oct 21, 2019
3,004
The article wrongly says a Ni-MH battery self-discharges in 1 week.
Oh Yeah? Modern (since 2005) Ni-MH cells use the Sanyo/Panasonic chemistry to hold a charge for 1 year.
 

jpanhalt

Joined Jan 18, 2008
11,088
I have two unmarked cells, circa 1.2V terminal voltage.
How can I tell which chemistry they are, and hence which charger to use?
Consider weighing them.

Various sources show that for the same physical size, NiMH weigh more than NiCd and alkaline is in between. For AA size, alkaline = 24, NiCd = 21, and NiMH = 27 (all weights in grams): https://power.tenergy.com/battery-size-chart/
 

Audioguru again

Joined Oct 21, 2019
3,004
Ni-Cad batteries are banned in many countries because Cadmium is a deadly toxin.
I found one 300mAh AAA Ni-Cad cell in a solar garden light from China snuck in by Walmart. It weighs 5 grams and a Chinese 300mAh Ni-MH AAA cell weighs 6 grams.
Both cells were dead so I charged them at the same time at the same current (in series) for 5 minutes. They both charged to full charge voltage and operated a solar garden light like with a full charge (charged in only 5 minutes at 90mA). They both felt like the same temperature.
 
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