Battery cost per kilowatt-hour calculator

Divide the purchase price by lifetime energy throughput: capacity times voltage times depth of discharge times cycle count times round-trip efficiency. Throughput is the only unit in which batteries can be compared fairly — 3,000 cycles at 100 percent DoD and 6,000 cycles at 50 percent deliver exactly the same throughput, so the apparent doubling of life is no such thing.

Because manufacturer cycle figures differ by a factor of five to six, the calculator refuses to guess this number. The depth of discharge the cycle rating refers to is mandatory — without it the figure is meaningless. If the rating is uncertain you can enter a range and get a cost band instead of a single value.

Then calendar life becomes the binding limit rather than the cycle rating: a cabin battery at 60 cycles a year would need 58 years to reach 3,500 cycles, and the calculator flags this. Capacity fade over life, temperature effects on ageing and residual value are not modelled.

In the reference case (100 Ah / 12.8 V, €160 market mean 08/2026, 3,500 cycles at 80 % DoD, η = 0.94) the throughput is 3,369 kWh — 4.75 ct per kilowatt-hour cycled, with a cycle-limited lifetime of 14 years. A brand unit at €800 lands at 23.7 ct on the same datasheet values — the premium buys warranty, service and vetted cells, not different cycles. Exactly why the market-range reference sits beside your price.

At low usage. A garden shed with 60 cycles per year reaches 3,500 cycles only after 58 years — the battery dies of calendar ageing long before, and the throughput shrinks accordingly. That is exactly the cross-check this calculator runs: it takes the minimum of cycle and calendar limits and reports when the calendar limit binds. Then the cheap AGM can indeed be the more economical choice.

Because cycle ratings vary by a factor of 6 between manufacturers — depending on test standard, end-of-life criterion (70 or 80% residual capacity) and cycle definition. With plausible lower and upper bounds (advanced assumptions) the calculator computes the cost span; in the reference case 22.2 to 33.2 ct/kWh. If the span exceeds the difference between two candidates, that is the honest answer: the data does not support a decision.

From the quarterly maintained dataset of the chemistry comparison: for the 100 Ah LiFePO4 class, retail prices in August 2026 ranged from €119 to €196. The range is a reference, not a calculation input — the maths always uses your price. Above it is not an error but a brand premium; below it, cell quality and warranty deserve a look.

Because the sample only covers the 12 V block class. A range for voltages nobody sampled would be a claim — the calculator omits the reference rather than extrapolating it. Your price and datasheet values work independently at any voltage.

Substantially. At the €160 market mean, a cycled kilowatt-hour costs 4.75 ct — for context, the spread between grid purchase and feed-in is around 23 ct. Storage itself is no longer the economic bottleneck; what matters is whether there is enough surplus to shift. The storage calculator checks that against your load profile.

Lifetime ends at the earlier of the two limits: cycles used up or calendar years over. In the reference case 3,500 cycles at 250 per year are reached after 14 years — one year before the 15-year calendar limit. At only 150 cycles per year you die by calendar: cycles remain unused, and paying for a higher cycle count does not pay off.

With caution. The calculator assumes datasheet cycles from new; a used cell has consumed part of them and keeps ageing calendrically. If you know the remaining cycle value from a capacity test, enter it — the market-range reference then does not apply, since it reflects new prices.