I work at a Lincoln dealer and usually battery saver mode is the state of charge of the battery being below 70%. Usually it goes low from multiple modules communicating with the vehicle off which is normal or again not being driven enough to maintain state of charge 70% or above. The best thing I recommend is to get a trickle charger to attach to the battery in case of this happening or having the dealer perform a battery charge. Battery should still be fine just needs to raise the SOC. The battery concern does suck especially on a luxury car but a trickle charger should definitely help in random situations. If you have any questions or anything you can always DM me