Lead-Acid vs Lithium Calculator

Lead-acid batteries degrade much faster when regularly discharged below about 50% of their rated capacity, so manufacturers and installers size lead-acid systems conservatively to protect their lifespan, effectively wasting half the rated capacity as a buffer. Lithium tolerates a much deeper 80% discharge without the same accelerated wear, so it needs proportionally less rated capacity — 1.25 times the usable energy needed, versus lead-acid's 2 times — to deliver an identical amount of usable energy.

Lithium's dramatically longer cycle life means it typically only needs installing once, or replacing far less often, across a 10-year comparison window, while lead-acid's much shorter cycle life usually forces multiple full replacements within the same period. Once total cost of ownership multiplies each option's initial cost by how many times it needs replacing, lithium's higher initial price is often more than offset by avoiding those repeated lead-acid replacement purchases.

A higher number of cycles per year shortens both batteries' expected lifespans proportionally, but it hits lead-acid's already-short cycle life harder in absolute replacement-count terms, since it starts from a much smaller cycle budget than lithium does. Applications that cycle very frequently, like daily solar self-consumption, tend to make lithium's cost advantage in total cost of ownership even more pronounced than applications that cycle only occasionally.

They answer slightly different questions — cost per cycle normalizes each battery's initial price against its rated cycle life independent of any specific usage pattern, which is useful for comparing the chemistries in the abstract, while total cost of ownership accounts for your actual usage rate and shows what you'd really spend replacing batteries over a specific time horizon. For a concrete purchasing decision, the 10-year total cost of ownership figure is generally the more directly actionable number.