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I’ve a bunch of Sanyo Cadnica cells of various capacities in my possession. Though they are a bit old they have never been used and are NOS. I’m currently trying to charge a KR-FH 7000mAh cell. As per the label on the battery(please see picture below) it says at 700mA it should be charged 14-16 hrs and at 233mA for trickle charge.

I’ve two questions:

  1. Currently the battery voltage is 0.89V since it sat in storage for like 5-7 years. So, I assume I can set the bench power supply to 700mA current and voltage to 1.45V. My power supply is CV type. But what if the battery was around let’s sat 1.09V or something like that where it’s not fully discharged? I’m aware a fully discharged elk is 1.0V usually.

  2. Is the tricky stage mandatory at 233mA after completing the 14-16hr charge at 700mA?

I’ve never manually charged a NiCD or NiMH cell. Only Lead Acid batteries so far. Usually the NiCD and NiMH batteries I’ve used at the AAA, AA and C type cells that have either it’s own automatic chargers. I do not have a charger for the 7,10 &20Ah cells. So manual charging is my only option for time being until I find something.

I’m hoping to get some expert opinions from you guys.

KR-FH 7000mAh Cadnica

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  • The "fully charged" voltage of NiCd cells is quite unpredictable so you cannot and should not rely on the voltage of the cells.

  • the C / 10 = 700 mA ( C = cell capacity, so 7000 mAh for the cell in the photos) is generally a safe current to charge a NiCd cell.

  • When a NiCd cell is full but you keep charging it, the cell gets warm. The C / 10 current is then usually a safe current as that means the cell will not get too warm.

  • If you want to fast charge, use a proper fast charger but since this is a non-standard cell size, such a charger might not exist.

  • Proper fast chargers fir NiCd cells monitor the voltage and the temperature of the cell. The voltage of NiCd cells drops by a very small amount just when it is fully charged. It is a property that can only be used when you monitor the very carefully, you need special equipment or a purpose designed circuit to use this safely.

Have you read this article at battery university?

When using a lab supply to charge such cells I usually set the supply to about 2 V per cell (you can charge several of same capacity in series) and set the current to C /10 or lower so that is takes a long time but this will safely charge cells that are still accepting a charge.

If a cell has a very low voltage, like 0 V, then sometimes you can bring it back to life by charging the cell with a large current of say 1 A for a short time, like one minute. If the cells after that still doesn't show a voltage of more than 0.5 V, it really is dead. Treat such cells as chemical waste as Cadmium is very toxic to humans (and that's why NiCd cells are now replaced by NiMh cells).

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