Calculate Peukert correction

Less than the rating suggests: with the Peukert formula t = H · (C_H / (H · I))^k, the reference case (C20 = 100 Ah, 10 A, k = 1.25) gives about 8.4 hours instead of 10, an effective capacity of roughly 84 Ah. The Peukert exponent should come from your datasheet — if it is missing, the calculator uses the chemistry's typical range and marks it as an assumption.

Effectively no: for LiFePO4 the exponent sits around 1.00 to 1.05, so the effect is negligible. The calculator switches the correction off for lithium and tells you why, instead of computing an effect that does not exist there. This avoids both common mistakes — applying Peukert to lithium (too pessimistic) and skipping it for lead (too optimistic).

No — it is valid only for a constant discharge current with the battery at rated temperature. Strongly varying loads such as fridge cycling or inverter surges, temperature effects and ageing are outside the model, and discharges faster than the one-hour rate fall outside the range where the approximation is established for lead.

A 100 Ah lead battery (C20, k = 1.25) delivers not 10 hours at 10 A but t = 20 · (100/200)^1.25 = 8.41 hours — effectively 84.1 Ah instead of 100. The naive C/I calculation overestimates runtime by 19%. At higher currents the error grows: at 50 A only about 56 Ah of the 100 Ah remain.

Because the capacity figure depends on the discharge duration: C20 means “measured over a 20-hour discharge” (5 A), C5 over five hours (20 A). The same physical lead battery shows markedly fewer amp-hours at C5 than at C20 — about 24% fewer at k = 1.25. A manufacturer stating “100 Ah at C5” therefore sells a larger battery than one stating “100 Ah at C20”. The converter makes both comparable; this is the most common hidden comparison error when buying lead batteries.

Practically not: k is around 1.00–1.05 for lithium chemistries, and usable capacity is nearly independent of discharge current — one of the real advantages over lead. The calculator then deliberately applies no correction, reports PEUKERT_NEGLIGIBLE and explains why. In the curve chart, ideal line and curve visibly coincide.

From the chosen chemistry's band midpoint: flooded 1.25 (band 1.2–1.3), AGM 1.10 (1.05–1.15), gel 1.15 — and the page shows this visibly as the dominating assumption. The datasheet value remains the better number, via the switch in the advanced assumptions. Until 5 August 2026 the form silently sent 1.25 for every chemistry — for AGM that cost almost an hour of runtime in the reference case (8.41 instead of 9.33 h) and suppressed the warning.

100 Ah (C20) at 10 A discharge: instead of the linear 10 hours, 8.41 hours remain — effectively 84.1 Ah, a 15.9 % loss, because discharge runs at twice the reference current. The same battery converted to C5 carries only 75.8 Ah. Planning C5 loads against C20 capacity compares apples with oranges — which is exactly what the reference-rate converter beside it is for.

Because the exponent there sits at 1.00 to 1.05 and the effect vanishes into noise: 100 Ah at 10 A remain practically 10.0 hours. Computing a “correction” that does not exist would be as wrong as omitting it for lead. The calculator explains the switch-off instead of hiding it — ruling out both common errors.

No. The relation describes constant discharge; it does not act during charging, and under strongly fluctuating load the calculation is only an approximation via the effective current. Inrush and peak currents belong to the C-rate calculator, mixed daily profiles to the runtime calculator with its load scenarios.

Because “100 Ah” without a reference rate is an incomplete statement: the same lead battery rated 100 Ah at C20 delivers only about 76 Ah at C5. Manufacturers pick the rate that yields the biggest number. The calculator therefore requires the rate and converts to another on request — only then are two datasheets comparable.