Battery Charger

Are they sealed or vented?

Guessing since the size is around "D" that you have 1.2V cells - but put a meter on each one and the bank itself to make sure!!

Are the 20 cells in parallel for higher mili-amp hour of your 1.2V system, or are they in series and you have a 24V bank?

Since each cell has 1.2V capability, if you have 20 in series you have 24V bank and would need to find a 24V DC charger...or you could have 10 in series each and those two banks in parallel and you'd have a 12V bank, and there are 1000s of 12V chargers on the market from mili-amp on up.

Here is a link on Ni Cad chargers: http://www.elecfree.com/electronic/nicad-charger-by-ic-ca3140e/

You should be aware that good Ni Cad cells when on full charge can reach 1.5 to 1.6 volts per cell. If this voltage is not attained you will not get max output from your cells and using a standard 24V lead acid charger will not do the job.

An automatic charger which detects the sharp voltage increase at the end of the charge and a temperature sensor to detect overheat which can occur from prolonged charging especially if one or two cells do not come up to specified voltages due to wear and tear. Also some of the better chargers have a timer function which calculates the charge given to the battery and shuts down to a holding charge when it thinks the cells have received the correct amount of charge.

Go to the advertisers websites and look for these points.

PS:- If you do not know the capacity of the cells, manualy charge one of the cells untill you aproach the voltages I mentioned then try a discharge of 4Amps for one hour after this time the voltage will drop reativly suddenly to 1V or less this is fully discharged and should not be run any lower. 4Ah cells are most common anything less than this is not worth bothering about for your application even 4Ah is not realy all that great.

A lead acid battery will most likely cause the cells to leak or even explode as the liquids inside turn to a hot gas......

LA Battereies are Votage charged, all others are (as far as I am aware) current charged. So most non LA batteries need to have current control and voltage sensing to ascertain when the battery is full.....

A good well designed charger will "see" when the battery is full and stop charging, no matter what the capacity is.

I personally would charge each cell as an individual (which they are) for the longest life span, probably impractical here, but still the best method to stop buying new batteries every few months!!