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RC Battery C-Rating & Continuous Current Calculator

Calculate safe continuous discharge limits, average throttle current, and expected flight runtime for your LiPo battery.

Quick actions: Save inputs, view saved runs, print, share, or export results

Saved Runs

Inputs

Battery capacity (mAh)

Battery C-Rating

Cell count (S series)

Motor max current draw (Amps)

Average throttle (%)

Results

Continuous Current Rating

99.0 Amps

Safety StatusSafe operation

Estimated Runtime6.1 minutes (to 20% state-of-charge)

Average Operational Current17.2 Amps

Operational Margin39.0 Amps

Total Stored Energy24.4 Watt-hours (Wh)

Tip

Save this tool to verify battery safety margins, calculate flight times, and avoid battery puffing.

Formula

LiPo battery power formulas

Continuous Current = (Capacity / 1000) × C-Rating. Average Current = Motor Max × (Throttle / 100)^1.8. Runtime = (Usable Ah / Average Current) × 60.

Uses nominal LiPo cell voltage (3.7V) and applies the standard 80% discharge limit safety buffer to protect lithium-polymer chemistry.

Step by step

How the calculation works

1Enter the battery nominal capacity in milliamp-hours (mAh).
2Provide the battery C-rating as marked on the label.
3Enter the cell count in series (S).
4Input the maximum continuous current draw of your motor (in Amperes).
5Set your average operational throttle percentage to estimate battery runtime.

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How to understand and use this calculator

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_(max) = (Capacity (mAh))/1000 × C_(rating). For example, a 2200mAh battery rated at 45C can supply: I_(max) = 2.2 × 45 = 99 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: Usable Ah = (Capacity (mAh))/1000 × 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_(avg) = I_(max_motor) × ( (Throttle %)/100 )^(1.8). The estimated runtime is then: Runtime (minutes) = (Usable Ah)/I_(avg) × 60. The safety margin is: Margin = I_(max) - I_(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, which models runtime using hover and active-flight current draw instead of a throttle curve.

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.

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.

How to understand and use this calculator

LiPo Battery Chemistry: C-Ratings and Discharge Limits

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: Usable Ah = (Capacity (mAh))/1000 × 0.80.

How to Use This Calculator

Worked Example: A 2200mAh 3S 45C Pack

Related Calculators

Once you know your flight time, cross-check it against the RC Flight Time Battery Power Calculator, which models runtime using hover and active-flight current draw instead of a throttle curve.

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.

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?+

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.

RC Battery C-Rating & Continuous Current Calculator

Inputs

Results

LiPo battery power formulas

How the calculation works

Learn more about this calculation

Understanding Calculator Formulas: How DTC Turns Inputs into Results

How to Use Do The Calculation Calculators: A Practical Step-by-Step Guide

RC Battery C-Rating & Continuous Current Calculator

Inputs

Results

Key output metrics

Current Draw & Safety Margin

How to understand and use this calculator

LiPo Battery Chemistry: C-Ratings and Discharge Limits

Calculating Runtime and Motor Load Margins

How to Use This Calculator

Worked Example: A 2200mAh 3S 45C Pack

Related Calculators

Related concepts

Frequently Asked Questions

LiPo battery power formulas

How the calculation works

Learn more about this calculation

Understanding Calculator Formulas: How DTC Turns Inputs into Results

How to Use Do The Calculation Calculators: A Practical Step-by-Step Guide

Key output metrics

Current Draw & Safety Margin

How to understand and use this calculator

LiPo Battery Chemistry: C-Ratings and Discharge Limits

Calculating Runtime and Motor Load Margins

How to Use This Calculator

Worked Example: A 2200mAh 3S 45C Pack

Related Calculators

Related concepts

Frequently Asked Questions