Tough question to answer. Off Grid means full charge and drain daily. Or partial charge and drain. Lithium batteries supposed to not develop a memory! Not 100% true! For the most part, YES! But the Off Grid is a tough life. Newer digital systems for battery use can increase life, but the rigors of very cold and discharge to depletion or near depletion are a tough environment. Calculating their safe use life is a shot in the dark. Everyone expects very long life. In reality it might be even longer or much shorter.