I recently got a few fluorescent lights and a couple fluorescent exit signs, some of which contain an emergency pack - low power DC ballast that runs the lamp (very underpowered) off a NiCd battery in case of power outage. Those were permanently powered (except a few power outages) so under permanent floating charge for the last 10 years or so, then taken out of service about 3 weeks ago and didnt see power since

I assume the batteries are drained right now, as the ballasts were probably running off them (although with the tubes removed) as the lanterns were taken down



In addition, i have two NOS latnerns of the same type with the same NiCd battery, that were made in 1999 and 2006, and never connected to power all this time



I am going to just store all the lanterns for now, and maybe put them to use in a few years but not before then

If any of the batteries are still any good, what is the best way to preserve them in intact condition ?



If i want to use NiMH batteries to replace the NiCd, only thing i am thinking is replacing the charging resistor in the circuit with higher value for lower charging current. Are there any other considerations ?

NiCd batteries don't suffering EOL or lower performance, as a result of complete discharging like lead-acid ones, so I think that you can charge them, and use them again.

They do - When the battery is flat there are crystals forming Spell of the Unknown inside, that eventually shorts out teh battery - then it won't take a charge, and will have very high self discharge

I want to prevent the batteries from going into this form of failure while the lanterns are not in use (but i can charge them periodically if thats what is needed)

Update - battery voltages measured

Taken down lights :
Nominal 4.8V

One measures 3V

Others 0V..1V



NOS from 2006 :
Nominal 4.8V

Measures 4.4V



NOS from 1999 :
Nominal 3.6V

Measures 0V

You really should keep the battery's charged to keep them in a good condition better still remove them and use them in other stuff and buy new ones for your lights when you are ready to use them. What ever you do don't leave them discharged

Thanks !

Will occasional charge + measuring the voltage once in a while suffice ? At what voltage level it is time to charge again ?

The batteries are sealed packs for the emergency light, i dont have any other application in which they can be used. I plan to keep the batteries alive as long as possible, and replace them when they fail for good

the ones at way less than 1v/cell are likely shot.
take then out now before they turn everything green.
make notes as to construction and dispose of them keeping the harness.
they have all been tricklecharged most of their life and are all tired.
should be easy to build new packs if you want to run them.most are sub c nicads.

Just put on charge part of the lights that had 0V in the batteries (the NOS one from 1999 and some of the used ones). So far they were charging for 10 minutes, and all except one already do light up for a few seconds (10 minutes worth of charge...) when i disconnect the power (they are supposed to get to full charge within 24..48 hours). The batteries may be intact

I will check if the one that does not work has a problem in the inverter first, and if its the battery, i will try few quick thunderbolt attacks with a car battery, it might revive it

Be careful mate I had some batterys like that leak and the liquid made my skin itch so if any of yours leak wash your hands straight  away

If they were in use in an emergency light, the most likely failure mode is water loss. The constant overcharging keeps them slightly pressurized all the time, so the gases (mainly the hydrogen) slowly leak away (through the imperfect seal,...), so can not form the water back.
If the lights were disconnected with still good batteries, but let to completely discharge them, the cells were most likely reversed (even one electrode reversal charge, so cell voltage below ~0.5V, means strong degradation). And if the cells were left in that state for long time, the dendrites form and that means short circuit, so cell death.

So if the cells do accept charge normally, they will still work fine.
But if they exhibit open and/or short circuit, they are really dead.
As someone already wrote, you may partially revive the shorted ones, but such revived cells would exhibit strong self discharge, so their usability I would see only as temporary fix, before new cells arrive...