I have a pack of four AA NiMH cells that came with my charger years ago and never used them. They're probably about 8 years old. I just opened them and they all test 0V...the charger doesn't even recognize them. Is there any way I can revive them? I tried applying 1.2V for about 30 seconds and still got nothing.

 

Your old Ni-MH battery cells are finished. Buy modern new ones.
Energizer guarantees their Ni-MH cells for 5 years, used or not.
For the last few years, most Ni-MH battery cells use Eneloop chemistry that come pre-charged and hold a charge for 1 year to 10 years.

 

Hello,

I have had mixed results with an old reflex charger based on the ICS1702 chip.
As the chip is obsolete, I will post a link to one that uses an ATtiny:
http://schematicselectronics.blogspot.com/2010/08/reflex-charger-batteries-nicd-and-nimh.html

Bertus

 

NiMH cannot be revived like the older NiCd batteries could be. The mode of failure is different.

More on the subject: https://batteryuniversity.com/learn/article/increasing_battery_power_by_zapping

 

About 40 years ago I needed to zap (2200uF capacitor charged to 15V) shorted Ni-Cad battery cells. The zap burns out the metallic whiskers that form inside. Ni-MH cells do not form metallic whiskers.

 

Rats.

 

Put a 20 ohm resistor in series with the battery and increase the applied voltage to get about 50-100mA of current (if you can).
Apply that for about an hour and then check the open-circuit battery voltage.

 

After an hour, still measures 0V...Oh well. Thanks.

 

One of life's great lessons. NiMH is not NiCd. Each has advantages and disadvantages. However with the advent of lithium chemistry cells, NiMH may still survive awhile longer. NiCd is almost out.