Reviving NiCd batteries

[kristiancyclist]

I recently received an old bicycle water bottle battery pack that is loaded with 11 NiCd batteries, approximately C sized. The entire pack registers a flat 0V. Is there any hope of reviving these batteries with a good charger? Or, should I recycle these batteries? I have no idea how old the batteries are.

I am hoping to keep the batteries alive. If not, then that's OK too. I can snip the battery pack off and get a new pack to put in it's place.

-- Boris

 

[worldedit]

I dont think the pack will recover. I will most likely not hold up the charge or start leaking.

 

[Mr Happy]

If it's NiCd and not NiMH you can try to revive it. NiCd can be stored at 0 V without harm, unlike NiMH.

You will probably want to do a conditioning cycle or two on the pack using a slow timed charge to bring it up to full voltage, then a discharge, then repeat until the capacity no longer shows improvement.

You will then want to see how well the pack holds its charge. If it shows a high rate of self discharge (perhaps because of metal whiskers inside some of the cells), then it is probably beyond rescue and will need recycling.

 

[Curious_character]

Adding to Mr Happy's posting, some of the cells might be shorted. They'll remain at zero volts after any length of charging time -- the voltage on good cells will come up to over 1.0 volt very quickly once you start the charge. Any shorted cells are dead and should go to recycling. You might come across methods of "zapping" a shorted cell to blow the short, but if you do this successfully you'll end up with a cell with a very high self discharge rate and the propensity to grow new short circuit paths in the future.

c_c

 

[jerry i h]

get one of those sophistaced [sp?] batt analyzers from Maha or La Crosse. They will give you exact answers. Suspect that most batts are still OK, but a couple are into le recycle place.

 

[linterno]

As worldedit said, the batteries could start leaking. It already happened to me with an old wireless phone batteries.

Some chargers like La Crosse BC-900 (I own one) refuse to charge 0V (I guess under 0.7 Volts) batteries.

Try this procedure:

- First check that the batteries are not short circuited. If short circuited stop here.
- Using an already charged battery, connect the discharged battery + to the charged + and the - to the - for 5 to 10 seconds. The charged battery will transfer some energy to the discharged one and you will get something closed to 1 volt. If you have a super capacitor (1 farad) try with this first instead of the charged battery.
- After that you can insert the discharged one in the battery charger.

 

[kristiancyclist]

It's a silly question, but how do I check for a shorted battery? Is it as simple as hooking up my Ohm meter across the terminals? I would imagine that the current from the Ohm meter would fight the battery and charge it slightly?

-- Boris

 

[Mr Happy]

It's a silly question, but how do I check for a shorted battery? Is it as simple as hooking up my Ohm meter across the terminals? I would imagine that the current from the Ohm meter would fight the battery and charge it slightly?

Yes it would charge it up slightly I think. I've never done this, but I might approach it this way:

1. Check the individual cell and make sure it is reading 0 V
2. Switch from volts to ohms and find out which test lead is positive (I assume it's the red one but this might not be certain)
3. Attempt a continuity test on the cell with positive to positive and negative to negative
4. If the cell is shorted, it will read close to zero ohms continuously
5. If the cell is good, it will charge up and eventually equal the meter voltage, at which point it will read high resistance

Another way is to attempt to charge the cell with a low current supply and see if its voltage increases. If you put a charge current through the cell and its voltage remains at 0 V then you know it is dead.

 

[Curious_character]

It's a silly question, but how do I check for a shorted battery? Is it as simple as hooking up my Ohm meter across the terminals? I would imagine that the current from the Ohm meter would fight the battery and charge it slightly?

-- Boris

I think a typical meter would generate such a small current that it would take a very long time to make any noticeable difference. You can, however, use it to check for a shorted cell. If the cell reads any voltage at all, it's not shorted. If it reads zero, it might or might not be.

What you need to do is run some current through the cell and see if the voltage comes up. If it's not shorted, it should come up almost immediately when a modest current is applied. A current of about 0.1C to C is appropriate, for example if the cells are 2000 mAh, this would be 200 - 2000 mA. You can get this current from a higher voltage power supply or battery with a series resistor, or from a constant current battery charger. (Virtually all NiMH and NiCd chargers are constant current.) Just watch the voltage with your meter for a while after you apply the current. If it stays at zero, the cell is shorted and it's recycle material.

c_c