Something I found:
http://www.oceannavigator.com/site/csrv/content.asp?id=639
Wet nicad cells use a dilute solution of potassium hydroxide (KOH) in water, with small amounts of lithium hydroxide (LiOH). This facilitates an alkaline reaction, rather than the acid reaction of a lead-acid cell. But, unlike the lead-acid cell, the nicad electrolyte acts only as an electron-transfer medium, and does not change chemically as the cell is charged or discharged. Therefore, a hydrometer cannot be used to monitor the state of charge (SOC). A metering system is needed for tracking SOC (which is of course more convenient). An accurate voltmeter is the minimum requirement, but ideally there should also be metering of current flow and an amp-hour calculation.
The voltage of a fully charged nicad cell is 1.65 volts, direct current (VDC), falling to between 1.00 and 1.15 VDC when fully discharged. Ten cells are therefore linked in series to make up a 12-VDC system. Nicad cells of various capacities are available that have the same voltage characteristics but differ in their amp-hour capacities and physical size. Cells linked in series should be identical (however, different strings of cells can be paralleled as long as the cells within each string are the same).
The cell you have pictured is TWO cells in series. That is why your seeing 2.47v.
Notice the two caps.
I have no idea where you can get replacement electrolyte.
Have fun.