Batteries at zero volts

Hey Ron,

I'm not qualified in electronics, nore do I have experience with such heavy cells, so at your own risk!

I work mostly with small digital devices like camcorders, digital cameras and media players, wich happen to have their own little power packs.
Dead batteries (or: declared dead by the charger wich is set to detect a minimum charge to work out how many cells (volts) to charge) are often revived by "forced tickle charging".
Usually I do that with a simple power supply that matches (+10-20%) the voltage. It often works, but dead by age or abuse equals dead forever.
I have a GP fast-charger (for Nimh AA) with a similar problem: a Nimh battery that has too low voltage will not be accepted. I have to slow-charge it first, and then it will go again.

Isn't Mik interested in some of your leftover good cells?
Keep'm charged in he meanwhile, will you?

First: I am interested in buying some spare cells for my Vectrix! There IS a cheap and easy way to attempt "resurrection" of your dead cells. Telephone me, at 301-439-3873, and I will provide you with options.--Bob Curry, Adelphi, Maryland-USA

I finally took a voltmeter to the 102 batteries I have sitting in my garage after disassembling the packs. 52 of them are at something above 1.0 volts, as expected. 50 of them, however, are at zero volts. I hooked up one of the zero-volt batteries to my charger, and the charger complained that the connection was broken, and refused to do any charging.

So are these zero-volt batteries completely useless now? Which isn't to say that the other 52 aren't useless in their own way...

Thanks,
Ron

Try to parallel a cell with some charge together with a 0V cell and see if the charger accepts that! Once a bit of charge has gone in, the "dead cell" might come back.

You could just charge the cells which have some voltage left and then use them to pre-charge the other cells.

Of course you know this, but make sure you connect positive to positive and negative to negative when you hook the cells together for pre-charging them with each other!

Whenever I have a problem with a AA or AAA NiMH cell being too low voltage for the charger, I just drop a better cell into the charger on top of it for a few seconds, that fixes it almost every time!

.

I usually try the gentle approach with a slow charge, but this might be the wrong procedure for totally empty cells.
Maybe anything works? The approaches seem to differ widely, but generally speaking, you don't know if the cells will come back until you have tried a few things.

Here is something from a PM I received a while back:

Having owned a lot of dead NiMH batteries from GM electric vehicles, this it how I was told to get a totally dead one going again. I have done this with 66 different 11 cell modules and it was sucessful all but once. The most important point was the initial charging step. The requirement was to monitor the voltage on all 11 cells in the module, then charge at the max capacity of my charger (75 amps) until all of the cells showed over 1.1 volt. This took a couple of minutes followed by a slow charge to 1.45 volts per cell. When the battery was fully charged, it was put on an electronic load and discharged at a 1C rate until the lowest cell in the module dropped to 1.00 volt. This was repeated several times (without the initial high current charge)until the cells equalized. It was explained to me that the intial high current charge was to "unlock" the cells and if this wasn't done, some of them might not start to charge before the other cells had reached final voltage which would lead to a permanantly un-equalized module. I don't know if this relates to the Vectrix cell but it sure worked for the GM traction batteries.

Very interesting! Maybe I'm all wrong about this. I have never tested any really really flat Vectrix batteries.
The ones I discharged myself were discharged to 0.4V at very low current, they immediately bounced back to almost 1.2V when the current was removed. At that point they needed a few minutes of slow charging before they could soak up current normally again.

Would you like me to post you pm anonymously for some reason? I think it might be a good contribution to the discussion!

No reason to post anonymously--Just don't want to add any confusion to the dead battery issue. Also I should add the slow charge was at 1/10 C rate and the discharge was up to 1 C limited by battery cooling. The more the modules were cycled, the better the various cell voltages in the module tracked during discharge. The reason for the "electronic load" is that it can hold a pre-set current level as the battery discharges. The constant current charge and discharge is important in this process for some reason. What makes NiMH batteries so attractive over lithium chemistry is the fact that the cell tends to go to low resistance when fully discharged vs. lithium that goes to high resistance. Whereas a NiMH can be stored totally dead, with terminals shorted (much like large NiCads) you will kill a lithium in an instant with low cell voltage. Some of the batteries had been fully discharged (0 volts terminal voltage) for several years and are now back in service. A dead lithium is a dead lithium--end of story. I have used this method on both Ovanic 85 AH and Panasonic EV-95 cells with great sucess. The reason for the PM is I didn't want anybody else out there trying this on the GP batteries as I have never done it on one of those--however, I would think this process would apply to them. Also, (and this doesn't apply to you) unless you have the proper equipment and understand what you are doing, you shouldn't try it. I don't want someone out there to put their car battery charger on one of these things and send it to the moon.

It sounds like these particular modules of 11 NiMH cells needed to be charged as whole modules.

On the Vectrix cells, however, you can charge each individual one which might give you more options!