Battery C-Rate Calculator

It means a charge or discharge current, in amps, numerically equal to the battery's capacity in amp-hours -- for a 100 Ah battery, 1C is 100 A. It's a capacity-relative shorthand specifically so the same "1C" label means "empties in one hour" regardless of whether the battery is a small 10 Ah pack or a large 1,000 Ah bank. Fractional and multiple C-rates scale from there: 0.5C is half that current (and roughly double the time), 2C is double that current (and roughly half the time).

Because many battery chemistries, lithium-ion especially, tolerate discharge current better than charge current of the same magnitude -- charging faster generates more internal heat and stress and can accelerate capacity fade or, in extreme cases, create safety risks, so manufacturers commonly rate a lower maximum charge C-rate than discharge C-rate for the same cell. This calculator lets you set Discharge C-Rate and Charge C-Rate independently for exactly this reason -- most real battery packs are not symmetric between the two directions.

Because power is current multiplied by voltage, and C-rate alone only determines current (relative to capacity) -- it says nothing about voltage. Two battery packs with identical capacity and C-rate but different nominal voltages will draw the same current but deliver very different power: a 48V pack delivers twice the power of an otherwise identical 24V pack at the same C-rate, since power scales directly with voltage for a fixed current.

Approximately, but not exactly -- this calculator's Discharge Time uses the idealized relationship time = 1/C-rate, which assumes the battery delivers its full rated capacity regardless of how fast it's drained. Real batteries, especially lead-acid chemistries, deliver somewhat less usable capacity at high discharge rates (the Peukert effect), so actual runtime at a high C-rate can be shorter than this simple formula predicts. Lithium-ion cells are much less affected by this than lead-acid, but manufacturer discharge curves are the authoritative source for a specific cell.