Solar Cost
Battery Cost per Usable kWh Calculator
Compare batteries on cost per usable kWh and per cycle
Updated 12 July 2026 · Live
What this tool does
Compares batteries fairly on cost per usable kWh, cost per cycle and cost per kWh over their rated life.
Enter the battery price, nominal capacity, depth of discharge and cycle life; the calculator returns cost per usable kWh, per cycle and over the whole life.
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Formula Used
How the battery cost per usable kwh works
Usable capacity is the nominal rating times the depth of discharge. Dividing the price by that usable figure gives the cost per usable kWh — the fair way to compare chemistries. Dividing the price by cycle life gives the cost per cycle, and dividing by usable capacity times cycles gives the cost of each kWh delivered across the battery’s whole life.
What you enter
Enter the battery price, nominal capacity, depth of discharge and cycle life; the calculator returns cost per usable kWh, per cycle and over the whole life. Every field is editable, and the result recalculates the moment you change a value.
Reading the result
Cost per usable kWh over life is the number that really matters: a cheap lead-acid battery with a shallow discharge and few cycles can cost more per delivered kWh than a pricier lithium unit. Compare like for like on that figure.
Safe by design
This calculator does the arithmetic of sizing — quantities, geometry and cost. It deliberately stops at the line a certified installer must sign off. It will never tell you a cable or fuse size, an earthing arrangement, a battery charge voltage, or a roof structural load: those are regulated calculations where a wrong number causes fire, electrocution or collapse. All electrical work must be carried out by a qualified, certified installer, and this page is not an installation guide.
Assumptions and limits
Cycle-life ratings assume a defined discharge depth and temperature; real life depends on how the battery is used. This ignores efficiency losses in and out of the battery and the slow fade of capacity with age, both of which nudge the true cost up.
Using it with the rest of BuildMetricLab
This calculator is one step in planning a system. Pair it with the other solar sizing, geometry and cost tools to go from an energy figure to a panel count, a layout and a costed bill of materials. Every BuildMetricLab tool runs entirely in your browser — no sign-up, nothing sent to a server, and the formula is shown on the page so the maths can be audited.
Sources & methodology
Compares batteries fairly on cost per usable kWh, cost per cycle and cost per kWh over their rated life. Every result is calculated from the values you enter, all inputs are editable, and no time-sensitive prices or tariffs are embedded.
Frequently asked questions
Why compare on usable kWh, not sticker price?
Only part of a battery’s nameplate capacity is usable, and that fraction differs by chemistry. Cost per usable kWh puts lithium and lead-acid on the same footing.
What is cost per cycle?
It is the price divided by the rated number of charge/discharge cycles — a rough measure of what one full cycle of the battery costs.
Why does lithium often win over life?
Lithium (LFP) tolerates deep discharge and thousands more cycles than lead-acid, so despite a higher sticker price its cost per kWh over life is usually lower.
Are efficiency losses included?
No. Round-trip losses and capacity fade with age both raise the real cost slightly above the figures shown.
Spotted something off?
Calculations or display — let us know.