Check C-rate and current loading

The C-rate is simply current divided by rated capacity, and on its own it is not a verdict: 1C is harmless for LiFePO4 yet borderline for a lead traction battery. That is why the calculator always checks against your battery's datasheet limits rather than a rule of thumb.

No — datasheets always state surge currents with a duration, for example 200 A for 30 s. The calculator therefore checks whether your load's start-up duration fits inside that window. A compressor start under three seconds is usually fine while a circular saw running continuously is not, and comparing current magnitude alone would give the same answer for both.

Without datasheet limits the calculator reports the C-rate but explicitly declines to judge it. It also does not cover internal resistance and voltage sag under load, cell imbalance, ageing, or several surges arriving in quick succession.

Because datasheets always state peak currents with a duration — “200 A for 30 s”. In the example case the compressor inrush of 180 A fits under the 200 A limit, but its 45 seconds do not fit the 30-second window: the battery is overloaded anyway. A calculator that only compares currents gives the same answer for a 3-second inrush and a continuously running circular saw — and is wrong in one of the two cases.

That depends on the battery, not the number: for LiFePO₄, 1 C discharge is usually uncritical (many datasheets allow 1–2 C continuously), for a lead traction battery 1 C is borderline to impermissible, and for charging lead batteries often tolerate only 0.1–0.2 C. That is exactly why this calculator never judges against rules of thumb but only against the limits of your specific datasheet — and without a limit it states the C-rate only, without judgement.

Because the charge limit drops markedly in the cold — and the cold season is exactly when charging must happen on short winter days. LiFePO₄ must not be charged below 0 °C at all, and reduced currents apply above that too. The temperature-corrected limit is the stricter of the two and the most commonly overlooked one; the calculator checks it separately.

Because they vary severalfold within the same chemistry: a 100 Ah LiFePO4 with a 100 A BMS allows 1C continuous, the same capacity with a 50 A BMS only 0.5C — and AGM datasheets quote anywhere from 0.2C to 1C for the same block. Without your limit the calculator states only the C-rate and says explicitly that the assessment is missing, rather than smuggling in a class assumption.

From the inverter calculator (largest inrush event plus base load) or from a measurement with an inrush function. Duration is the harder value: compressor starts stay under three seconds, motors under load can take ten times longer. In the reference case it is 45 seconds — and that, not the current level, is what fails the check.

That the BMS may cut out before the start-up completes — mid spin-up. The remedies, in sensible order: reduce the inrush (soft starter, the appliance's soft-start mode), a larger battery or one with a wider surge window, or parallel blocks sharing the current. A bigger inverter alone does not help — the limit sits in the battery.

Because many datasheets state the charge limit only for 25 °C and derate below — and charging happens exactly when it is cold. The field is prefilled with the datasheet limit; if you know the manufacturer's curve, you tighten it deliberately. The check then reports the colder limit as the binding one.

Yes, with one conversion: with n equal blocks the current ideally divides by n — the per-block C-rate remains current per block over block capacity. In practice it only divides evenly with symmetric cabling; the parallel-connection calculator checks exactly that symmetry. Unequal blocks do not belong in parallel.