# NiCd Batteries rapid drops in voltage?

I have 7 NiCd batteries hooked up in series (ordered from china) for a spare time project of rebuilding an old battery drill. Have been trickle charging them with 8.7V and 0.04A. When the battery is full it shows 8.6V The thing is when I hook it up to the drill the voltage rapidly in like 1-2 seconds goes from that to 8.0 also the amperage goes from 1A to 0.7A drawn from the batteries. Have been researching these kinds of batteries and it seems that rapid voltage drops are not their thing. Am I doing something wrong or is it possibly a problem with the batteries.

Technical specs: Drill is a Bosch 8.4V all I could find on the net. Batteries are NiCd stack of 7 each 1.2V and 600mAh.

• Dead cells are a common failure mode of these types of battery. – Ignacio Vazquez-Abrams Jul 24 '17 at 17:46
• So do you think that I have a dead cell in a whole new battery assembly ? Might be since they were cheap and from china. – Angel Pejev Jul 24 '17 at 17:48
• Putting things in series means that if one thing breaks, the whole thing breaks. The more things you got in series the greater the chance that it happens. – Harry Svensson Jul 24 '17 at 17:48
• Dropping from 8.6 volts fresh off the charger, to 8.0 volts with a 1 Amp draw seems reasonable to me. I think a 1 Amp draw on a 600 mAh battery is a bit much... – Peter Bennett Jul 24 '17 at 18:15
• NiCd batteries should be charged with a current limited supply and not a constant voltage. You can charge indefinitely at C/10h, where C is the Ah capacity. e.g., 800 mAh cells can be charged indefinitely at 80 mA. – Transistor Jul 27 '17 at 7:50

NiCd battery should use 1.4V to charge per cell. So 7 cells would be 9.8V.

The 8.4V charger is meant for Lithium battery.

• I will make a simple current limiting charger at 9.8V and 100mA and tell you about the results. Thanks for the help. – Angel Pejev Jul 27 '17 at 14:56

Ni-Cd type batteries mainly divide into two categories: Low Maintenance Type and Maintenance-free type.

So as I understand from your description and the Ah rating, I assume your batteries do not require any maintenance.

For maintenance-free Ni-Cd batteries, two-level charging regimes are possible:

Single level charge

1.42 +/- 0.01 V/Cell


Two-level charge

Float level: 1.42 +/- 0.01 V/Cell
High Level (Boost): 1.45 +/- 0.01 V/Cell


So in your case, 7 x 1.42= 9.94 V should be applied to the battery group.

Also another thing I assume you did not use these batteries and stayed uncharged for a long time. If that is the case you can apply Commissioning charge to batteries (7 x 1.55 = 10.85V) for 48 hours which is normally a procedure when you normally charge them for the first time after your purchase but it also works for storage batteries.

The batteries are rated at 6/10 of an amp, and the drill may take 2 or 3 amps under load at 2 amp draw 6/10ths won't last long.

• The batteries are rated 600mAh. That is a much different thing than being rated 600mA. Note that little h. That makes it a rating of capacity rather than saying how much current it can deliver. I'd be surprised if a 600mAh battery could deliver over 600mA continuously, though. The smaller cells usually have a higher internal resistance that keeps you from drawing really high current from them. – JRE Aug 8 '17 at 16:47