This is one of the umpteen software problems that Garmin would fix if someone in the bowels of that apathetic company knew how its products were used in the real world. They do not and it will never be fixed although the relevant engineer could write the code in a working lunch.
An alternative solution to your problem might be to charge a batch of eneloops every weekend in a suitable charger and swap the cells every day, twice a week, or however often is needed to guarantee power in your use. Eneloops don’t mind sitting with a full charge, don’t self-discharge, don’t mind being fully discharged, don’t mind being partially charged from any depth of discharge, and are otherwise among the most reliable batteries of any chemistry I’ve used. Accept no substitutes.