It works on a "first inserted, first loaded" principle.
The right charger bay integrates a refresh option.
After an extended period of use, the shown percentage of remaining power from batteries differs from the actual percentage after charging. With the refresh bay this error can be automatically corrected.
NOTE: This is a direct replacement for the GKL221 charger.
Leica Accessories Brochure
Leica Batteries and Chargers Brochure
Leica Batteries and Chargers Technical Specification
Leica GKL341 Charger - User Manual