Lithium batteries are not suitable for constant recharge cyclng, like a super capacitor or a lead-acid car battery, constantly recharged by vehicle alternators.
Lithium batteries lose capacity after each recharge, and fail after a few thousand cycles. If the lithium cells are arranged as First Charged First Discharged (FIFO), rather than First Charged Last Discharged (FILO), then the First cells charged are discharging First & suffering all the cycling wear & tear, while the rest of the battery gets little use.