I was wondering if anyone with the right hardware has attempted to recharge the Energizer Ultimate Lithium cells. I was doing some reading and found some interesting information at: http://books.google.com/books?id=ZwD8uTpXet4C&pg=PA516&lpg=PA516&dq=nasa+l ithium+iron+disulfide&source=bl&ots=l_lbu3l5fy&sig =3c2cBvA0ifgzQVzHhFdlok1tW44&hl=en&ei=az6qTvmYE6Hj 0QHr3vnNDw&sa=X&oi=book_result&ct=result&resnum=3& ved=0CC0Q6AEwAjgK#v=onepage&q=nasa%20lithium%20iro n%20disulfide&f=false

Page 516 and especially 517 show that a side chemical reaction takes place once the cell reaches 2.4 volts or so and needs to be avoided. After more Googling it appears that they use 2.25 volts as the cutoff voltage when charging the high temperature versions of this battery chemistry.

I ask because my brother gave me 2 Energizer Ultimate Lithium cells from his portable GPS unit that he had drained and I figured I would do some research and experimentation. I measured the voltage on each cell and one of them was completely dead at 1.5 volts open circuit and dropped to 0 under load. The other was at 1.65 volts yet and was still able to produce a bit of current yet. I grabbed the cells, the DMM, and an old but wonderful HP adjustable power supply outside on some brickwork in my back yard. I set up the power supply to limit to 2.25 volts and 20 mA of charge current and charged each cell individually. The mostly dead cell charged up mirroring the discharge curve and terminated after 6 days, which indicates that nearly the entire cell capacity went in. The completely discharged cell was charging up at 0.1 to 0.2 volts higher than the other one and it was fluctuating where it would increase and then decrease, increase, decrease in voltage over and over again as it charged. After 7 days, this cell too finally charged up, but I think its suffering from partial internal leakage as the OCV slowly decreases over time over several days from 2.25 volts to 2.0 volts. The first cell dropped to 2.14 volts and has held there now for 2 weeks with no decline. I have not yet attempted to discharge them yet to check capacity. They do power my Maglite AA however and charged right back up after this test. I will be doing discharge capacity tests soon when I get some more time.

Based on the tests I have done so far and my understanding of the chemistry, I'm guessing the completely discharged cell is probably toast as a full discharge will completely dissolve the lithium electrode and when recharging, it doesn't really have anything to plate out on, which would also help explain the higher charge voltage on that cell too and possibly some dendrite shorts popping through the separator. So if you want to recharge these cells, do not run them down 100%. I expected the cells to short out via dendrites when I attempted to charge them (which is why I did this outside) but I was shocked at how smoothly the one cell took charge. I'm sure they won't last through too many charge cycles however before the lithium electrode completely disintegrates and/or the cell shorts out.

I am checking to see if anyone else with the right gear has done anything similar with these cells and could compare notes.