[EDIT - based on additional info. from Howard Riehl]The original batteries used1974-2002 were Varta(brand) 50 ma Ni cads.Also Yuasa(Japanese) made Nicad batteries were used. The nominal voltage is 2.4 volts total....1.2 volts from each cell. From 2003 forward Varta 80 were used, 80ma. The Varta V80 and V80H(high temp) are NIMH also rated at 1.2 volts per cell.
www.mouser.com,among other has a big assortment of batteries that would work and fit. order something and they will send their cataloge, which is a lot easier to navigate than their site.