Battery C-rate calculator
A battery must deliver the current your loads draw, not just store enough energy. The C-rate (load current ÷ capacity) tells you whether your draw is safe for the chemistry. Pull too hard, especially from lead-acid, and you lose capacity (Peukert effect), generate heat and shorten life.
Safe C-rates by chemistry
| Chemistry | Comfortable sustained rate | Notes |
|---|---|---|
| LiFePO4 / Li-ion | ~1C (often more) | Handles high continuous draw well; surge limited mainly by the BMS. |
| AGM / Gel | ~0.3C | Tolerates higher bursts than flooded, but sustained high draw shortens life. |
| Flooded lead-acid | ~0.2C | Above this the Peukert effect cuts usable capacity sharply and the bank runs hot. |
These are comfortable sustained limits, not hard cliffs — brief surges (a motor starting) are usually inverter-limited and last under a second. The real concern is continuous draw causing heat and capacity loss. If your continuous C-rate is too high, the fix is a larger bank (which lowers the rate) or a higher-current chemistry.
Frequently asked questions
What is a safe C-rate for a lead-acid battery?
Flooded lead-acid is comfortable up to about 0.2C sustained, AGM and gel up to about 0.3C. Above that the Peukert effect reduces usable capacity and the battery heats up. Brief surges are tolerated but sustained high draw shortens life.
What C-rate can LiFePO4 handle?
LiFePO4 comfortably sustains around 1C continuous, often more, which is why it suits high-draw loads like microwaves and pumps far better than lead-acid of the same capacity.
How do I lower my battery's C-rate?
Increase the bank capacity (more Ah lowers the C-rate for the same load) or switch to a higher-current chemistry such as LiFePO4.
Looking for a definition or a quick answer? See the solar & battery glossary for terms used on this page, or the FAQ for common sizing questions. For the full explanation, read the C-rate guide.
Sources & standards
- Victron Energy — Battery Capacity and the Peukert Exponent — Manufacturer technical explainer on why usable capacity falls at higher discharge (C-)rates.
- UL 1973 — Batteries for Use in Stationary and Motive Auxiliary Power Applications — Safety standard most LiFePO4 and other stationary/portable battery packs are certified to.
- IEC 62619 — Safety Requirements for Secondary Lithium Cells and Batteries for Industrial Applications — International safety-testing standard for LiFePO4 and Li-ion (NMC) cells used in stationary storage.
Educational estimate. See the methodology.