Your LiPo says 120C on the label but sags below 14V on punch-outs and comes down hot. That 120C number? It’s marketing, not engineering. C-rating is one of the most abused specifications in FPV — and most pilots don’t know how badly they’re being lied to until a pack puffs mid-flight. Here’s the reality, the math, and how to buy batteries that actually deliver.
What C-Rating Actually Means
C-rating is a multiplier applied to a battery’s capacity (in amp-hours) to estimate its maximum safe current delivery. It is not a hard limit — it’s a manufacturer’s claim about thermal performance at a given discharge rate.
The formula: Max Current (A) = Capacity (Ah) × C-Rating. A 1300mAh (1.3Ah) pack labeled 100C theoretically delivers 130A continuous. In practice, independent testing shows most “100C” packs deliver 30-45C sustained before voltage sag exceeds healthy thresholds. The label C-rating is a fantasy number.
Burst C-rating (typically listed as “150C burst” alongside “100C continuous”) specifies what the pack can deliver for 1-3 seconds without immediate damage. Think of it as the overhead for punch-outs and quick throttle blips. Sustained burst-current draw — like a 10-second full-throttle climb — will cook a pack even if you’re within the printed burst rating.
Step 1: Calculate Your Build’s Real Current Draw
Don’t guess. Use a current sensor (onboard ADC or external clamp meter) to measure peak current during a full-throttle punch-out. A typical 5-inch racing quad on 2207 1950KV motors with 5-inch props pulls 100-120A at full throttle. That means your battery needs to deliver at least 120A sustained — not burst — for the flight style to match the pack.
Step 2: Derate the label C-rating by 50-60%. A “120C” LiPo from a reputable brand (GNB, Tattu, CNHL) typically delivers 45-55C in real testing. A no-name “150C” pack might deliver 25C. Apply this derating, then calculate: a 1300mAh pack at 50C real delivers 65A. If your build pulls 120A, that battery is undersized by nearly half — no wonder it sags.
Step 3: Check for puffing after flight. A pack that’s warm but firm after a flight is within its limits. A pack that’s soft, puffed, or hot to the touch (above 60°C / 140°F) is being pushed past its real C-rating. Continued use in this state leads to internal resistance increase and eventual cell failure.
Matching C-Rating to Flight Style
Racers need the highest real C-rating — full-throttle spikes are constant and sustained. A 1500mAh 6S pack from a racing-oriented line (Tattu R-Line, CNHL Black Series) is the right call. Freestyle pilots can get away with slightly lower ratings since throttle modulation is intermittent. Long-range pilots can use lower-C packs (20-30C real) because current draw is typically 5-15A cruising. Weight matters more for long range, and higher-C packs are heavier for the same capacity.
LiPo C-Rating Reality Check
| Manufacturer Claim | Real Continuous C-Rating (Independent Testing) | Usable Current (1300mAh Pack) | Flight Style Suitability |
|---|---|---|---|
| 70C | 30-35C | 39-45A | Cruising, long range |
| 100C | 40-50C | 52-65A | Freestyle, moderate racing |
| 120C | 50-60C | 65-78A | Aggressive freestyle, racing |
| 150C | 55-65C | 71-84A | High-end racing (top-tier brands only) |
| 200C+ | 60-70C (optimistic) | 78-91A | Marketing fiction; no pack tests above 70C sustained |
What Most Pilots Get Wrong About C-Ratings
Mistake 1: Comparing C-ratings across brands. A 100C from GNB is not the same as a 100C from a random Amazon brand. C-rating has no industry standard measurement — each manufacturer defines it differently. The only way to compare is independent testing (check RC Groups battery test threads) or real-world flight data.
Mistake 2: Ignoring capacity when choosing C-rating. A 1500mAh pack at 50C real delivers 75A. A 1300mAh pack at 50C real delivers 65A. Same C-rating, different total current — because the C multiplies capacity. If you need more current, increasing capacity (mAh) at the same C-rating is more effective than chasing a higher C-rating number.
Mistake 3: Using burst C-rating as the selection criteria. Burst ratings are for sub-3-second events. If your typical flight involves 5+ second full-throttle climbs, continuous C-rating is the only number that matters. Buying based on burst C-rating is how you cook packs in 20 cycles.
Mistake 4: Flying packs that have already puffed. A puffed pack has permanently increased internal resistance. The C-rating it can deliver drops with every cycle after puffing begins — and thermal runaway risk increases. Retire puffed packs to low-current duty (bench testing, goggles power) or recycle them.
⚠️ Regulatory Notice: The flight recommendations in this article should be followed in accordance with the latest 2026 drone regulations in your country or region. Always verify local laws regarding flight altitude, no-fly zones, remote ID requirements, and registration before flying. Regulations vary significantly between the FAA (US), EASA (EU), CAA (UK), CAAC (China), and other authorities.
Whether you’re freestyling or pushing laps, the right battery changes everything. As we covered in our LiPo storage and discharge guide, proper storage voltage and cycling discipline extend pack life significantly — good habits make those expensive high-C packs last 200+ cycles instead of 50.
Once you understand C-rating, the next step is tracking your packs’ health over time. Our LiPo IR testing guide shows how to measure internal resistance — the single best predictor of real C-rating delivery. A pack with rising IR is losing its ability to deliver current, regardless of what the label says.
If you’re seeing voltage sag despite a properly-rated pack, head to our FPV voltage sag troubleshooting guide for the full diagnostic workflow. Sometimes the problem isn’t the battery at all — it’s a cold solder joint or undersized XT60 connector adding series resistance.
For pilots running 6S builds pulling 120A+ on punch-outs, the CNHL Black Series 1300mAh 6S delivers tested 55-60C real continuous current with minimal sag. One of the few packs where the label isn’t complete fiction. Worth the premium if your build demands real current delivery.