matthewkleinmannMy friend gave me this battery pack that had been sitting in his basement for a couple of years. I took the screws out and carefully took the case apart. Inside of the case was a plastic jig to hold the batteries together, a small potted module that I am assuming was both the brain for the charge state indicator lights, and the over current disconnect circuit, and 7 FSPE70045 cells. From what I read on the net, these were discontinued in 2009 so they are at least 11 years old. But they were free.
The pack was surrounded in blue foam tape, and sadly, it was good quality blue foam tape, and it did not come off easy. I spent a long time trying to get it to roll off the plastic, cell interconnects, and cells themselves but time and heat helped the adhesive get a very positive grip. In the end I wound up doing a lot of scraping and getting the foam and adhesive off in little balls.
Once the blue foam was removed it was easy to see that there was a flex pcb that wrapped around the pack and had a connection to monitor every cell in the pack. This was easily removed with a soldering iron and a bit of wiggling of the flex PCB until the tab on the cell was pulled from the hole in the flex pcb.
The next step was removing the strapping holding all the cells in series. This was woven through the plastic jig holding the cells in place. I found it easiest to start with one of the first cells and grab the tab with some needle nose pliers and roll the tab off the top of the cell, snapping the spot welds as it rolled. Note, if you try this with a battery pack with any charge at all on it, be very careful not to short out the cells! One by one I rolled the interconnect off of the cells until they were free. Than it was just a matter of figuring out how to open the plastic cage. I did not figure that out but I was able to push on a cell and get it to slip past the cage and once one cell came out there was a lot more room for it's brothers to follow.
After getting all of the cells out, once of the has a decided nasty streak on it like something leached out of it. The rest look brand new. Being sealed up in that battery pack kept them looking nice and pretty. They were all pretty much stone cold dead.
My first attempt at charging them was in my friends smart charger. It found the cell I put in, tried putting 280 MA through it for a minute, and errored out. My guess is that the smart charger is assuming the cell is near or above the knee in the discharge curve, and it did try and push some current into the cell, but the the voltage rise on the cell was not fast enough, and it assumed a bad cell. Not one to give up I created a litlte jig with some aluminum foil, clip leads and a variable current limited power supply. The first order of business is you do not want to put more than 4.2V across one of these. I set the veneer voltage knob to half way and the course voltage up to 3.8V, than used the veneer to land it right on 4.0V. These are Chinese voltmeters so I figured best to error a bit on the side of caution. Next, from the datasheet the maximum charge rate is 7.4A but again I don't wanna make anything smoke, so I dialed the current limiter all the way down, shorted the output leads on the power supply, and dialed it up to 1 amp even.
I am not the most arts and crafts like person in the world, but I did see a panavice sitting on the bench and with that and some aluminum foil I made a very make shift holder for one cell. I ran clip leads from the power supply to my foil contacts and sat back and watched. At first the current was pegged at an amp, and there was very little voltage across the cell, but bit by bit the current started to ebb down and the voltage across the cell started to go up. Man that sounds like a battery charging to me! After an hour or so there was not a lot of current flowing and over 3V across the cell. I took it off my makeshift charger and put it back on the smart charger. This time it recognized it as a battery, and is trying to pit 750ma through it. I am leaving the rest of the charge cycle in it's little micro controllers hands. In the meantime I got anther one on the bench supply, and much like the last one the current is slowly going down and the voltage is slowly going up.
When the smart charger is done with the first one, I will replace it with the second one and put the first one on the active load and see what it's capacity is etc, and discharge it. Hopefully this time the smart charger will be able to bring it back to life without any intervention. I will keep you posted on the progress, but so far, contrary to what I have read on the net, it does in fact seem possible to bring a naturally self discharged lithium battery back from the dead..
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After an overnight on the smart charger it was telling me the first two cells were topped off. Sadly, sometime over the last year we managed to loose the ac adapter for the smart load. I was going to discharge one of them at a mild rate and see what the capacity was. That has yet to happen. On the flip side, the cells just sat on the table for a week or more. I got curious the other day and I wondered what the terminal voltage on them was after just sitting. I was very disappointed. The best of them had under 2V on them. Apparently self discharge is an issue. This does jibe with them developing little fingers on the inside that short them out. However I am a bit stubborn and at some point in the near future I plan on putting them back on the bench supply again and doing another round with the smart charger. I am wondering if the go rounds with the smart charger will fry off the small internal shorts. The cells only got slightly warm to the touch when I had the 1A consent current limited to 4V going into them.
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This project ended up being scrapped. Sadly. Where I was at the time I no longer had a place to play with them. I do think I could have improved on them though. I am dubious about bringing them back to like new though. Still there is a range between totally dead and like new. For example even if they were only a medium fraction of their capacity, they would run my solar watering system for a long time on an overcast day when the plants in the greenhouse often get no water at all (I am not sure that is entirely a bad thing), but if is it could be mitigated. So I may revisit this again sometime in the future.