I thought all Spotmatics used a bridge circuit and were not sensitive to voltage variations. My non F model is fine with alkalines as is my SP500.
It's easy to tell. If the meter position for proper exposure is in the centre and the meter needle goes to that position when the meter is switched off, then it's a bridge circuit and an alkaline or silver 1.5 volt cell will do.
The meter in a bridge circuit displays the difference in voltage between two potential dividers. At correct exposure, this difference is zero so it cannot vary with cell voltage.
If the exposure is set by lining up one needle with another then it is not a bridge circuit and will be sensitive to voltage change