Walk down any FPV battery aisle and you’ll see 100C, 120C, 150C ratings on packs that cost $25. These numbers are marketing, not engineering. A true 120C 1300mAh pack would deliver 156 amps continuously without sagging below 3.5V per cell — and I’ve tested enough batteries on a programmable load to tell you: almost none of them do. Here’s how to read through the label and buy packs with actual performance, not inflated specs.
What C-Rating Actually Means
C-rating is a multiplier applied to capacity to determine maximum safe discharge current. A 1300mAh (1.3Ah) pack rated at 45C can theoretically deliver 1.3 × 45 = 58.5 amps continuously. At 90C burst, it can deliver 1.3 × 90 = 117 amps for short pulses (typically 5-10 seconds).
The keyword is “theoretically.” Real C-rating depends on cell chemistry, internal resistance, age, and temperature. A brand-new pack at 25°C will deliver much closer to its rated current than the same pack at 5°C — cold LiPos have 2-3x higher internal resistance, which means more voltage sag and less usable current.
The temperature factor: LiPo chemistry operates best at 30-40°C. Below 15°C, internal resistance doubles. Below 5°C, it triples. A 100C pack flown in winter behaves like a 30C pack — not because the label is wrong, but because cold chemistry can’t move lithium ions fast enough. Pre-warm packs to room temperature if you fly in cold weather.
Continuous vs Burst: The Fine Print
Every C-rating has two numbers: continuous and burst. Continuous is what the pack can sustain from full charge to storage voltage (roughly 3.8V/cell resting). Burst is what it can deliver for 5-10 second spikes — punch-outs, recovery from dives, full-throttle passes.
What burst actually costs: A burst discharge heats the cells internally. If you do ten 5-second punch-outs on a pack, cell temperature rises from 25°C to 45°C. At 50°C+, permanent capacity loss begins. At 60°C+, the pack starts gassing and puffing.
A practical rule: your build’s maximum amp draw should be at or below the pack’s continuous C-rating. Burst rating covers transient spikes, not repeated abuse. If your 5-inch quad pulls 120A at full throttle and your pack is rated 45C continuous / 90C burst with 1300mAh capacity: continuous rating delivers 58.5A — you’re doubling it. This pack will sag heavily, run hot, and lose capacity within 30 cycles.
Parameter Table: LiPo Selection by Build Type
| Build Type | Typical Max Draw | Recommended Capacity | Minimum Continuous C-Rating | Real-World Equivalent |
|---|---|---|---|---|
| Tiny Whoop (65mm 1S) | 6-8A | 300-450mAh | 30C (9-13.5A) | 300mAh 30C HV |
| Toothpick (2.5-3″) | 15-25A | 450-650mAh 3S | 45C (20-29A) | 550mAh 70C (labeled) |
| 3″ Cinewhoop | 20-35A | 650-850mAh 4S | 60C (39-51A) | 850mAh 75C (labeled) |
| 5″ Freestyle | 80-120A | 1300-1550mAh 6S | 75C (97-116A) | 1300mAh 100C (labeled; real ~45C) |
| 5″ Racing | 100-150A | 1100-1300mAh 6S | 100C (110-130A) | 1100mAh 120C (labeled; real ~50C) |
| 7″ Long Range | 30-50A | 2800-4000mAh Li-Ion 6S | 10C Li-Ion (28-40A) | 3000mAh Molicel P42A 6S1P |
The labeling reality: I’ve tested packs labeled 120C that deliver a true continuous C-rating of 40-50C. The label isn’t lying per se — it’s using a different measurement standard (often “the cell can deliver this current for 0.5 seconds before voltage drops below 3.0V/cell,” which is not useful). For practical purposes, halve the labeled continuous C-rating to estimate real sustained performance.
How to Test Real C-Rating
Method 1: Internal resistance + temperature rise. Measure IR with a dedicated IR meter (or charger with IR readout). A healthy 1300mAh 6S cell should show 3-8 mΩ per cell at room temperature. Fly the pack hard for 2 minutes, land, immediately measure IR again. If IR jumps from 5 mΩ to 15 mΩ, the pack can’t sustain the current draw. Good packs show <50% IR increase between cold and hot states.
Method 2: Voltage sag under known load. Arm your quad, hover at exactly mid-throttle (check OSD throttle percentage), note the voltage sag from resting. A 1300mAh 6S pack at 25.2V resting that sags to 22.5V at hover (3.75V/cell) has moderate IR. If it sags to 21.0V (3.5V/cell), the pack is tired or mislabeled. Compare against a known-good pack of similar capacity.
Method 3: Capacity discharge test. Fully charge to 4.2V/cell, discharge at 1C (1.3A for 1300mAh) to 3.3V/cell on a charger with discharge mode. The mAh delivered should be ≥95% of label capacity. Below 90% = the pack has significant cycle wear. My 2-year-old practice packs deliver 80-85% of original capacity — they still fly but with noticeably more sag.
Common C-Rating Mistakes
Mistake 1: Buying the highest C-rating available. Higher C-rating packs use thinner electrode layers that pack more surface area into the same volume, but they weigh more and age faster. A 150C 1300mAh pack weighs 220g; a 75C pack of the same capacity weighs 195g. That 25g difference is noticeable on a 650g quad. Buy the C-rating your build actually needs.
Mistake 2: Ignoring pack weight. A heavier pack requires more thrust to hover, which draws more current, which needs a higher C-rating — it’s a positive feedback loop. Ultralight builds (sub-250g) benefit more from a lighter pack with appropriate C-rating than from a heavyweight “race” pack.
Mistake 3: Using the same pack for racing and freestyle. Racing demands the highest C-rating you can get — every millisecond of sag costs time. Freestyle benefits from a pack that handles repeated burst cycles without overheating. Race packs optimized for peak current sacrifice cycle life; freestyle packs optimized for durability sacrifice peak current.
Mistake 4: Letting packs sit fully charged. LiPo chemistry degrades fastest at full charge (4.2V/cell) and high temperature. If you’re not flying within 24 hours, storage-charge to 3.8V/cell. Packs stored at 4.2V for a month lose 3-5% capacity permanently.
As we covered in our guides on LiPo internal resistance testing and LiPo storage and maintenance, understanding your batteries’ health is the foundation of reliable FPV. C-rating is just one piece of that puzzle.
⚠️ 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. LiPo battery transport and disposal are subject to hazardous materials regulations — check your local requirements for shipping and recycling. Regulations vary significantly between the FAA (US), EASA (EU), CAA (UK), CAAC (China), and other authorities.
The UAVModel Pro 1300mAh 6S 100C LiPo is independently tested at a true continuous 55C with IR under 5mΩ per cell — no inflated numbers. Ideal for 5-inch freestyle builds. Available on our FPV batteries page.