C Rating in LiPo Batteries: Selecting the Right Power Output for Your Application

If you’ve ever stared at a LiPo battery label wondering what the big “C” number means, you’re not alone. The good news: once you connect C rating to capacity, it becomes straightforward—and you can choose batteries confidently without risking brownouts, overheating, or disappointing performance.

Quick promise: by the end, you’ll be able to calculate the current (amps) your pack can safely deliver, pick a suitable C rating for drones, RC cars, robotics, or IoT projects, and avoid the most common beginner traps.

The 60‑second explanation

• Capacity is how much “fuel” the battery stores, measured in mAh or Ah. 1000 mAh = 1.0 Ah.
• C rating tells you how fast that stored energy can be delivered as current.
• Core formula: I_max (A) = C × Ah.
  • Example: A 1500 mAh (1.5 Ah) pack with 60C can supply 60 × 1.5 = 90 A (theoretical continuous) if the rating is honest.

For a clear primer on C rates and how 1C corresponds to a one‑hour discharge, see the concise overview by Power‑Sonic in their battery C‑rate explainer.

Continuous vs. burst (and why burst is tricky)

• Continuous C rating is what the pack can sustain without overheating or damage.
• Burst (or peak) rating is for very short spikes. Many hobby packs don’t define how long “burst” lasts; community practice often assumes on the order of a few to ~10 seconds, but this is not standardized. Treat burst as a safety cushion for quick throttle punches, not a number you run at for long. See this community discussion referencing short‑duration bursts in the PX4 ecosystem: “short periods such as 10 seconds” (community context).
• Marketing reality: C labels—especially burst—can be optimistic. Prioritize continuous ratings, then add headroom and verify in your own setup by checking temperature and voltage sag. A practical introduction for FPV beginners that echoes this approach is the FPVFC LiPo beginner’s guide.

Voltage sag and internal resistance (plain‑English)

Every battery has internal resistance (IR). When current flows, some voltage is lost inside the pack:

• Voltage drop: V_drop = I × R_internal
• Heat generated: P_heat = I² × R_internal

Higher current → more voltage sag and heat. If you pull near a pack’s limits, you’ll see the voltage dip under load and the pack get warm. Accessible background on IR and its effects is covered in BioLogic’s educational note “What is internal resistance in a battery?”. For a practical, rider‑oriented view of sag behavior under load, see Ride1Up’s battery voltage sag explanation.

A simple, reliable selection framework (7 steps)

1. Gather your system info
   • Voltage (cell count like 2S/3S/4S), motor/driver max current, typical current, connector type, desired runtime.
2. Estimate max current draw (I_max)
   • Sum motors/servos and consider ESC or driver limits. Use worst‑case “all at once” cautiously—some systems rarely hit absolute peaks.
3. Choose a capacity (Ah) that fits your runtime and weight goals
   • More capacity increases runtime but adds weight, which can raise current in flight/acceleration.
4. Compute required continuous C
   • C_required = I_max / Ah
5. Add headroom so the battery runs cool and sags less
   • Drones/RC cars: target 1.3× to 2× the calculated C_required.
   • Hobby robots: 1.2× to 1.5×, depending on stall‑current exposure.
   • IoT: often 0–20% headroom on C; focus on low ESR cells and capacity for standby.
6. Check connectors and wiring
   • Small connectors like JST‑PH are only for low currents (around 2 A); larger connectors like XT30/XT60 handle much higher. Verify the connector and wire gauge ratings exceed your expected current.
7. Validate in the real world
   • Do a short full‑throttle or worst‑case test. If the pack gets hot to the touch or voltage sags too much, upgrade C or capacity, or reduce the load.

Worked examples (with quick math)

These examples are illustrative; your exact numbers may differ. The method stays the same.

1) 5‑inch FPV drone (freestyle)

• Estimate: Total current peaks 120 A (common on modern 5″ quads), typical hard flight 80–100 A.
• You choose 1500 mAh (1.5 Ah) for weight and balance.
• Required C for the estimated peak: C_required = 120 A / 1.5 Ah = 80C.
• Recommendation: Pick a reputable pack labeled in the 70–100C range and verify temperature after aggressive pulls. If it lands very warm or you see big sag, consider a higher‑C pack or slightly more capacity.
• Context: Hobby guides commonly report these draw ranges for 5″ quads; see Oscar Liang’s LiPo battery guide for FPV for typical behaviors and practical tips.

2) 1/10‑scale RC car (brushless)

• Estimate: Peak 120 A during hard acceleration, typical 40–60 A while running.
• You choose 5000 mAh (5.0 Ah) for good runtime.
• Required C for the peak: C_required = 120 A / 5.0 Ah = 24C.
• Recommendation: Choose ≥30–40C continuous to reduce sag and heat during repeated launches. Also ensure your ESC and connectors can handle peaks; modern race ESCs often have very high peak ratings (e.g., the Hobbywing XR10 Pro line lists triple‑digit peaks—check your specific model’s datasheet).

3) Small hobby robot (DC gearmotors + servos)

• Estimate: Two small gearmotors plus servos can hit a worst‑case 12 A combined during stalls.
• You choose 2000 mAh (2.0 Ah) to keep size/weight manageable.
• Required C: C_required = 12 A / 2.0 Ah = 6C.
• Recommendation: A 10–20C pack is generally sufficient. Important: If the robot runs 2S/3S LiPo, regulate down to proper servo voltage (5–6 V) and account for servo stall currents.

4) IoT sensor with LTE bursts

• Estimate: LTE‑M/NB‑IoT radio peaks around 1.25–1.3 A during transmit bursts, with a much lower average. Digi reports up to 1.25–1.3 A peak on the XBee 3 Global LTE‑M/NB‑IoT module depending on variant (see the Digi XBee 3 LTE‑M/NB‑IoT datasheet, power requirements).
• You choose a 1000 mAh (1.0 Ah) pouch cell.
• Required C (for peaks): C_required = 1.3 A / 1.0 Ah = 1.3C.
• Recommendation: A quality 3–5C cell with low ESR usually handles these pulses. Place ceramic decoupling plus a small bulk capacitor near the module to avoid brownouts during bursts.

Choosing headroom without overdoing it

• If you regularly hit hard bursts (FPV, RC car launches), aim higher on C or capacity. Both reduce sag because higher‑C and larger‑Ah packs often have lower effective internal resistance.
• Don’t overspec wildly for flying models: higher‑C packs tend to be heavier. Extra weight can negate some performance gains and reduce flight time.
• For ground robots and cars, the weight penalty may be less critical; prioritize cool operation and consistent voltage.

Connectors and wires can be the bottleneck

Even if your battery can deliver high current, small connectors or thin wires may heat up and drop voltage.

• JST‑PH is common on small LiPo pouches and is typically rated around 2 A with 24‑AWG wire; see the official JST PH datasheet (2 A with AWG #24).
• XT60 is widely used for medium‑to‑high current in RC; AMASS publishes mechanical/electrical specs (including contact resistance and temperature range) in the XT60 manufacturer datasheet. Community practice treats it as suitable around the 60 A class when properly soldered with appropriate wire gauge.
• XT30 commonly serves lower‑to‑mid currents (roughly tens of amps depending on build and wire). When in doubt, step up connector size and use thicker silicone wire.

Also consider wire gauge ampacity. Industrial silicone‑insulated cable data (e.g., Eland Cables’ high‑temperature silicone cable datasheet) shows how allowable current depends on cross‑section and temperature. Hobby use is variable, so be conservative.

Charging, storage, and cutoff basics (safety first)

• Use a proper LiPo balance charger with the correct cell count (S) and chemistry setting. A conservative rule is to charge at ≤1C unless the manufacturer explicitly allows higher. Battery University’s long‑running reference on Li‑ion charging outlines standard CCCV practices in BU‑409 – Charging Lithium‑ion.
• Don’t charge unattended and avoid charging on flammable surfaces. A LiPo‑safe bag or nonflammable container adds a layer of protection.
• Storage: Keep packs around 3.7–3.85 V per cell (roughly 30–60% state‑of‑charge) in a cool, dry place. See the guidance compiled in Battery University BU‑702 – How to Store Batteries.
• Cutoff: Many hobbyists set under‑load cutoffs around 3.3–3.5 V per cell to preserve life and reduce risk of cell reversal. Don’t deep‑discharge—resting below ~3.0 V/cell risks damage.
• Inspect regularly: Stop using packs that are puffy, damaged, or unusually hot. Retire questionable packs safely.

Common beginner mistakes (and easy fixes)

• Treating burst as continuous: Don’t. Size to continuous current, use burst only for short spikes.
• Trusting optimistic labels: Prefer reputable brands and continuous ratings; add headroom and validate by checking heat/sag after a hard run.
• Forgetting mAh → Ah conversion: 2200 mAh = 2.2 Ah. Use Ah in I = C × Ah.
• Ignoring connectors/wires: Tiny connectors or thin wires can overheat and cause big voltage drops.
• Over‑discharging: Running packs down too far hurts lifespan and can be unsafe. Use timers, telemetry, or low‑voltage alarms.

Quick checklist (print or screenshot)

• [ ] I know my system voltage (S count), connector type, and desired runtime.
• [ ] I estimated max current (sum of motors/servos/drivers) and typical current.
• [ ] I chose a capacity (Ah) that fits weight/space.
• [ ] I calculated C_required = I_max / Ah and added appropriate headroom.
• [ ] My connector and wire gauge are rated above expected current.
• [ ] A short worst‑case test shows acceptable temperature and minimal sag.
• [ ] I follow safe charging, storage, and cutoff practices.

常见问题

• Is a higher C rating always better? Not always. Higher‑C packs are often heavier and more expensive. Choose “high enough” to stay cool with minimal sag; beyond that, gains may be marginal for your use.

• My pack voltage sags a lot under throttle—what should I check? Consider a higher‑C pack, larger capacity, shorter leads, better connectors, and ensure your pack is healthy. Internal resistance increases with age and abuse.

• Can I rely on burst C for my design? No. Treat burst as emergency headroom. Design around continuous current.

• Charging C vs. discharging C are the same thing, right? Different. Charge rate “C” refers to how fast you charge relative to capacity (e.g., 1C charges a 2000 mAh pack at 2 A). Discharge C is about how much current you can draw. Unless your manufacturer says otherwise, stick to ≤1C charging. See the fundamentals in Battery University BU‑409.

• What about cell count (S) vs. C rating? “S” controls nominal voltage (e.g., 3S ≈ 11.1 V), while C × Ah controls current capability. You need both voltage and current to match your system’s needs.

You’ve got this

Pick a capacity that fits, compute the C you need, add some margin, and sanity‑check with a short stress test. Keep an eye on temperature and sag, respect connector limits, and follow safe charging and storage habits. If you do those things, LiPo batteries will feel a lot less mysterious—and your projects will run stronger and safer.