Off-Grid Solar Calculators

Battery storage

Battery C-Rating & Max Discharge Calculator

C-rate is discharge current relative to capacity. 1C on a 100 Ah pack is 100 A. Inverters, trolling motors and induction loads can exceed a cheap BMS even when the watt-hour math looks fine.

Inputs

Ah

Many drop-in LiFePO4 packs are 0.5C continuous; some power packs are 1C or more.

System voltage of the battery or series string.

A

DC current you intend to draw. Leave a small number if you only want the pack limit.

Results

Max continuous current
50.0A
Max continuous power
600W
Hours at max C-rate
2 h
Load C-rate
0.40

Planned load divided by capacity. Keep this at or below the pack C-rate.

Recommended gear

Engineering methodology

Maximum continuous current I_max = C-rate × capacity in Ah. Maximum power P_max = I_max × V (from P = V × I). Hours at that current = 1 / C. Load C-rate = load amps ÷ capacity. Always use the BMS or cell continuous rating, not a peak burst figure.

Frequently asked questions

What does a 1C battery rating mean?

1C means you can discharge the full rated amp-hours in one hour: 100 A from a 100 Ah pack. 0.5C is 50 A from that pack and would theoretically empty it in two hours at that current.

Why do many LiFePO4 drop-in batteries use 0.5C continuous?

Cell heating, busbars and the BMS current limit often cap continuous discharge around 0.5C even if cells can burst higher. Exceeding the continuous rating can trip the BMS or overheat the pack.

How do I convert a watt load into a C-rate?

Current I = P ÷ V (Ohm’s-law power form). Load C-rate = I ÷ Ah. Example: 1,200 W on 12 V is 100 A; on a 100 Ah pack that is 1C.

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