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   Recovering old batteries

          Conditioners that do a three cycle charge / discharge run are ok for recovering relatively new batteries that may have been  mistreated ...radios
          left on, or trickled continuously for weeks. I don't find them very good for recovering really old batts.

          It is useful to know what happens when they discharge so I usually data log a 1 amp discharge from "fully charged". I then usually see a 1.2 volt
          voltage step that indicates that one cell has low capacity. This can sometimes be cured by the "conditioner".

          More often with the very old batteries i find that one cell (or more) is "stuck" at zero volts. So fully charged shows about 1.3volts low (the approx
          voltage of a fully charged NiCad.) The conditioner will not normally "unstick" these. I use a current limited power supply (a Kingshill actually)
          and apply a change of around 3 amps (for AA cell packs up to 1200mAhr) for a period of about 10 seconds...no longer and then allow a resting
          period of 20 seconds for the temperature to dissipate. This needs to be done until the battery terminal voltage rises to the right value and does not
          drop too rapidly when the charging voltage is removed. I do not recommend you do this as it is possible if the pressure inside the battery increases
          to have the cell explode with some violence (but I am still alive and I'm a coward !).

          Once the battery seems to hold the right terminal voltage put it one a normal charger, preferably at the C/20 rate and overcharge by 100% i.e. 28
          hours .instead of 14 hrs. Once the battery has been recovered to reasonable terminal voltage then cycling it with rapid charge / discharge, will get it
          back to some sort of usable capacity with luck. It doesn't work on every battery but it is well worth trying. You may find that a battery recovered
          like this will work when taken from the charger but may not hold charge as well as a new battery. This is probably due to whiskers across the plates,
          some rough treatment will improve things sometimes. Modelers seem to be able to use batts like this and they charge the cells in a few minutes (in
          a poly bag in a bucket of water !! ) and also flatten them as quickly.

          The ideal way to recover cells is individually rather than in series across the the series string, but this is not always possible. I have re-celled laptop
          batteries by just replacing the faulty (stuck) ones, it is not recommended as the capacity should be balanced but it is a cheap experiment and it often
          works when it is not economic to pay £100 for a replacement for an old machine.

Thanks to Alan G3 NYK
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