The two batteries are wired in series within the detector. Depending on type of cells you use the Open Circuit voltage (OCV) and nominal voltages are different specifications to look at. THIS INFORMATION IS PER SPECIFICATION SHEETS AND IS NOT WHAT THE ATX WAS DESIGNED TO. The best answer might be obtained by a phone call to Garrett.
Per IEC/ANSI Standards:
Alkaline manganese cells have an OCV of 1.65 and a nominal voltage of 1.5
Carbon zinc cells have an OCV of 1.80 and a nominal voltage of 1.5
Nickel Cadmium cells have an OCV of 1.5 and a nominal voltage of 1.2
With the above information and the number of cells (
the design of the detector's internal regulator should be designed to handle the maximum potential voltage of the Carbon Zinc cells. I.e. 14.8VDC (OCV) and a Nominal Voltage of 12VDC.
One more specification to look at is the higher the mAh rating of the NiCd, the larger the cells will be in length and diameter.
The larger ones in some battery holders make for a very tight fit especially in the Garrett Infinium.
Also using the larger cells in a battery holder made for minimum specifications of an Alkaline cell will cause the holder to fail.
AA-Rechargable (in mm) Length 47.3 min 50.5 max Diameter 13.5 min 14.7 max