# RC Battery C-Rating & Continuous Current Calculator Calculate safe continuous discharge limits, average throttle current, and expected flight runtime for your LiPo battery. --- - **Canonical URL:** https://dothecalculation.com/calculators/rc-battery-c-rating-calculator - **Category:** Hobbies & Leisure Utilities - **Publisher:** Do The Calculation (https://dothecalculation.com) - **Cost:** Free, no account or sign-up required - **Privacy:** Runs entirely in the browser; inputs are never sent to a server - **Methodology:** https://dothecalculation.com/methodology --- ## Calculate battery C-rating and discharge margins Compute safe continuous current discharge limits, average throttle current draw, and runtimes for LiPo batteries. - Continuous current amp capacity solver - Throttle-curve runtime projections - Safety margin load warning alerts ## LiPo Battery Chemistry: C-Ratings and Discharge Limits Lithium Polymer (LiPo) batteries are the standard power source for RC models due to their high energy density and discharge rates. The C-Rating represents how fast a battery can be safely discharged relative to its capacity. The maximum continuous current (in Amperes) is calculated as: \(I_{\text{max}} = \frac{\text{Capacity (mAh)}}{1000} \times C_{\text{rating}}\). For example, a 2200mAh battery rated at 45C can supply: \(I_{\text{max}} = 2.2 \times 45 = 99\text{ Amperes}\) continuously. Exceeding this limit causes overheating, internal damage, gas buildup (puffing), and potentially fire. ## Calculating Runtime and Motor Load Margins To protect the battery and prevent cell damage, LiPos should never be discharged below 20% of their total capacity (the 80% rule). The usable capacity is: \(\text{Usable Ah} = \frac{\text{Capacity (mAh)}}{1000} \times 0.80\). Current draw scales non-linearly with throttle. We model average current draw using an exponent of 1.8 to reflect brushless motor efficiency curves: \(I_{\text{avg}} = I_{\text{max\_motor}} \times \left( \frac{\text{Throttle \%}}{100} \right)^{1.8}\). The estimated runtime is then: \(\text{Runtime (minutes)} = \frac{\text{Usable Ah}}{I_{\text{avg}}} \times 60\). The safety margin is: \(\text{Margin} = I_{\text{max}} - I_{\text{max\_motor}}\). A positive margin indicates safe operation. ## How to Use This Calculator Enter your battery's capacity in mAh and its C-rating (both printed on the battery label), its cell count (S rating), your motor's maximum current draw in Amps, and your average throttle percentage for a typical flight. The calculator returns maximum safe continuous current, energy capacity in Wh, average current draw, estimated flight time, and safety margin. ## Worked Example: A 2200mAh 3S 45C Pack With the calculator's defaults — a 2200mAh battery rated at 45C, 3S cell count, a motor with a 60A maximum draw, and an average throttle of 50% — the maximum continuous current the battery can safely supply is 99A (2.2Ah × 45C), giving a healthy 39A safety margin over the motor's 60A maximum. At 50% average throttle, the non-linear power curve means actual average current draw is only about 17.2A (well below the 60A peak), giving an estimated flight time of roughly 6.1 minutes on the battery's 80%-usable capacity of 1.76Ah. ## Related Calculators Once you know your flight time, cross-check it against the [RC Flight Time & Battery Power Calculator](/calculators/rc-flight-time-calculator), which models runtime using hover and active-flight current draw instead of a throttle curve. ## Frequently asked questions ### What is a battery C-rating? A multiplier indicating the maximum rate at which a battery can be discharged relative to its capacity. ### How is maximum continuous current calculated? Multiply battery capacity in Amp-hours (mAh / 1000) by the C-rating. ### What is the 80% rule for LiPo batteries? A safety rule advising you to only discharge 80% of a battery's capacity to prevent voltage drops that damage cells. ### Why does throttle percentage affect current non-linearly? Brushless motor power demands scale cubically with RPM, meaning current draw increases rapidly at high throttle settings. ### What cell voltage indicates a discharged LiPo? A cell is fully discharged at 3.0V under load, but should rest no lower than 3.7V. ### What is nominal voltage per cell? The standard rating of 3.7V per cell for standard LiPo batteries. ### What is cell count (S)? The number of cells wired in series. A 3S battery has 3 cells and a nominal voltage of 11.1V. ### What causes a LiPo battery to puff? Over-discharging, drawing too much current, or overheating causes the electrolyte to decompose, releasing gas. ### How do you calculate battery energy in Wh? Multiply capacity in Amp-hours by nominal voltage (3.7V times cell count). ### What is a safe current margin? The difference between the battery's max continuous current and the motor's peak draw. A positive margin is required for safety. ### Should I match the battery C-rating exactly to my motor's max draw? No — leave headroom. Motors often briefly exceed their rated draw under load spikes (hard acceleration, punch-outs), so most pilots target a continuous current rating comfortably above the motor's stated maximum. ### Does average throttle percentage during a flight matter more than peak draw? Yes for runtime estimates. Peak draw determines whether the battery is safe to use at all, but average throttle over the flight determines how long the charge actually lasts. ## Related concepts - **Lithium Polymer cell chemistry** — Volumetric and gravimetric energy density characteristics. - **Brushless motor efficiency curves** — Current draw scaling across throttle ranges. - **Usable depth of discharge (DoD)** — Managing state-of-charge to extend battery lifespan. ## Related guides - [Understanding Calculator Formulas: How DTC Turns Inputs into Results](https://dothecalculation.com/blog/site-guides/understanding-calculator-formulas) — Understand how Do The Calculation formulas are presented, what the explanation blocks mean, and how to verify calculator logic before using a result in a real decision. ## Related calculators - [Model Rocket Aerodynamic Drag & Apogee Calculator](https://dothecalculation.com/calculators/model-rocket-drag-apogee-calculator) — Simulate rocket flight to calculate peak altitude, apogee, drag coefficient, and maximum velocity using numerical integration. - [Crochet Blanket Size & Yardage Calculator](https://dothecalculation.com/calculators/crochet-blanket-dimensions-calculator) — Calculate the yarn yardage, skein count, and finished blanket weight based on your stitch density, gauge, and yarn class. - [Geocaching Coordinates Distance & Bearing Solver](https://dothecalculation.com/calculators/geocaching-distance-bearing-calculator) — Solve the exact distance and compass bearing between two GPS coordinates, or project a new waypoint using the Haversine formula. - [Photography Exposure Value & Reciprocity Calculator](https://dothecalculation.com/calculators/photography-exposure-value-calculator) — Calculate Exposure Value (EV) and EV100, and compensate for film reciprocity failure during very long exposures in photography. - [Telescope Dawes' Limit & Resolving Power Calculator](https://dothecalculation.com/calculators/telescope-resolving-power-calculator) — Calculate telescope magnification, Dawes limit, Rayleigh criterion, and field of view based on your aperture and eyepiece. - [Wood Shrinkage & Seasonal Movement Calculator](https://dothecalculation.com/calculators/wood-shrinkage-radial-calculator) — Model exact wood shrinkage and seasonal dimensional changes based on relative humidity, temperature, and wood species type. --- _This calculator is for educational and planning purposes. Always verify measurements, conversions, and material requirements before making purchases or physical builds._ --- _Source: [Do The Calculation](https://dothecalculation.com/calculators/rc-battery-c-rating-calculator). Quote freely with attribution and a link to this page._