La Crosse Technology RS-900 Instruction Manual page 28

THE SIZE C AND SIZE D BATTERY ADAPTERS (FREE ACCESSORY)
The battery adapters are used for connecting the AA battery to the electric devices requiring
Size C or D batteries. To apply the adapter:
1. Install the AA battery to Size C or Size D adapter as below.
The AA battery used with the
Size C adapter
60
The AA battery used with the Size D
adapter (it is required to place the
battery into the "C" adapter first
and then the "D" adapter)