It expresses current as a multiple of capacity: a rate of 1C empties a pack in about an hour, 0.5C in about two. It lets packs of different sizes be compared on how hard they can be worked, rather than in amps that mean nothing on their own.
The C-rate is a piece of notation rather than a property, and it turns up on datasheets exactly where the important limits are.
What the notation means
A rate of 1C is the current that would discharge the rated capacity in one hour. Half that rate takes about two hours; twice it, about half an hour. Charging rates use the same convention, and it is where the fast-charge claims on this shelf are actually specified.
Why it matters for sizing
An inverter’s demand translates into a current the battery has to supply, and whether that is comfortable depends on the pack’s size. The C-rate makes the comparison directly: the same inverter is a modest load on a large bank and a maximum-rate demand on a small one.
What the limits are set by
On lithium packs, by the battery management system, which enforces maximum charge and discharge currents regardless of what the cells might tolerate. Those published limits are the ones that apply, and they are often the binding constraint on the whole system.
Where it shows up in real specifications
Charge rate claims, discharge limits, and capacity figures quoted at a named rate. When a capacity is given without its rate, the omission matters: the same pack measured gently and measured hard gives two different numbers.
Where this page and the manufacturer’s documentation differ, the documentation is the one to follow. Every capacity, output, input window, current limit, cycle count and temperature threshold on this page comes from the maker’s own published figures, with the unit as printed and the source named. None of it is measured here, and no figure is converted into another convention, because a converted number is a different number. And for any cycle count: the number is set by two qualifiers — the depth of discharge tested and the capacity the pack must still hold at the end. Change either and the same cells produce a different headline. This page reports the qualifiers wherever a maker publishes them, and says they are missing when they are not.
What people ask before they order
Why not just quote amps?
Because the same current is gentle on a large pack and severe on a small one. Expressing it relative to capacity makes the figure portable between products.
Does a high discharge rate cost capacity?
On most chemistries, yes — the faster the discharge, the less total energy comes out, and makers who publish capacity at more than one rate are showing the effect rather than hiding it.
Last reviewed 16 September 2026