HP-9114B IL disk drive - how to prolong battery life?

[Martin Hepperle]

• Lead (Pb) batteries (e.g. the Panasonic block mentioned above) want to be kept at a relatively high state of charge. It is not good to drain a car battery completely.
  Usually it is good to regularly recharge them - e.g. for the HP 110 it is recommended to recharge when the indicated charge falls below 60-80%. One should never overcharge or leave them on the charger for long time.
  I regularly recharge my lead batteries every 2-3 months for about 6-14 hours, but not much longer. I do not actually have a timetable for this, but I do it regularly. If in use for more than an hour or so, I plug in the charger, especially the 9114 draws more current that the charger can supply.
• NiCd batteries on the other hand like to be cycled completely (but not deep discharged!). Otherwise they suffer from "memory effect".
• NiMH batteries seem to be close to NiCd but obviously don't need the cycling. They loose capacity slower than NiCd and Pb when not used.
  

Overcharged NiCd and NiMh batteries get warm - Pb batteries may open their pressure valve and you may hear them breathing. Both not good and charging should be stopped. Overcharged LiPos may halt and catch fire...

The HP chargers are primitive by today's standard.
Therefore I use, if possible, a small r/c model aircraft charger which has programs for NiCd, NiMH, LiPo and Pb batteries.
The best is to use such a special charger for the specific battery type. Mine was about 50$ - it is not necessary to spend 300+$. It operates on 12V, so I use my laboratory power supply.
For NiCd it also has a "cycle" option where you can specify 1...3 discharge/charge cycles).
These chargers "know" about the battery chemistry and when the battery is full. Usually the voltage increases and when the battery is full it drops slightly and the energy is converted into heat. These "intelligent" charger then switch off.

Some HP chargers have very simple diode rectifiers (sometimes a single diode), which leave a pulsating voltage and current, which is probably also not the best for charging batteries. In the best case they reduce charging current to a "trickle" for Pb batteries, but not as prcise as a modern charger.

I built me a small box with contacts which can take the refurbished NiCds or NiMH packs e.g. from the ThinkJet. For the 9114 disk drive I crated an adapter cable.

But even so, I agree that after maybe 5 - 6 years it may be necessary to replace batteries.

Martin