Five NiCds implies what charging voltage?

[broggerp]

Off the wall, but I know where to go with such questions. ;-)

I've an ancient (10+ yrs old) vinyl inflatable mattress with a (theoretically, once upon a time) rechargeable blower to fill/empty it.
I seem to have lost its wall-wart charger.
Inside I see no circuitry, an on-off switch, and a female charger port wired across a stack of five C-size NiCds.
There is no explanatory diagram label or embossed to indicate the charging voltage and polarity.

First guess: Would that be a 12-volt, DC charger?

Of course, the other question: the thing has *never* been charged or used. Are the batteries likely to work?

Thanks for any input,

Paul B.