The C-rating printed on a LiPo battery is one of the most misunderstood numbers in the FPV hobby. It looks simple — a bigger number must be better — but the reality involves burst ratings, voltage sag, and a surprising amount of marketing. Understanding what the C-rating actually tells you will help you pick the right pack, avoid puffing your batteries, and get more punch out of every flight.
What the C-Rating Actually Means
The C-rating describes how fast a battery can safely discharge relative to its capacity. A 1C discharge drains the entire pack in one hour. A 50C rating means the pack can, in theory, discharge at fifty times its capacity. To convert that to amps, multiply the capacity in amp-hours by the C-rating. A 1500mAh pack (1.5Ah) rated at 100C can supposedly deliver 150 amps. That is the number that matters for a high-draw FPV quad.
Calculating Safe Discharge Current
To find the theoretical continuous current of a pack, take the capacity in milliamp-hours, divide by 1000 to get amp-hours, and multiply by the C-rating. A 1300mAh 75C pack works out to 1.3 times 75, or about 97 amps continuous. Compare that to what your motors actually draw at full throttle. If your quad pulls 120 amps on punch-outs but your pack is only rated for 97, you are asking the battery to deliver more than its continuous rating every time you pin the throttle.
Burst vs Continuous Ratings
Here is where marketing sneaks in. Many packs list both a continuous and a burst rating, and the burst number is often double the continuous figure. Burst ratings apply for only a few seconds at a time and assume the pack starts cool. A 150C “burst” label on a pack that can only sustain 75C continuously is not lying, exactly, but it is not the whole story. Always size your build around the continuous rating, and treat the burst figure as a short headroom, not a target.
How C-Rating Affects Voltage Sag
When you ask a pack for more current than it can comfortably deliver, the voltage sags. That sag is visible in your OSD as the battery voltage dropping hard during punch-outs. Severe sag robs you of power exactly when you need it, heats the pack, and can trigger a premature low-voltage warning or even a brownout on the electronics. A higher true C-rating means less sag under load, which translates directly to sharper throttle response and more consistent power through the whole flight.
Choosing the Right C-Rating
A good rule of thumb is to pick a pack whose continuous rating comfortably exceeds your quad’s maximum current draw. If your build peaks at 100 amps, look for a pack rated for at least 120 to 130 amps continuous so you are not running at the ragged edge. Heavier, higher-C packs carry more current capability, but they also weigh more, so there is a real trade-off for racing. Freestyle and racing pilots usually land on 100C-class packs, while long-range and cruising builds can often use lower-C, lighter packs.
Signs You Are Over-Stressing a Pack
A battery that is being pushed past its rating will tell you. Watch for excessive voltage sag on punch-outs, a pack that comes down warmer than usual, or swelling (puffing) after hard flights. Any of these is a sign that the pack is working beyond its comfort zone — either upgrade to a higher-C pack or lighten the load. Consistently over-stressing a LiPo shortens its life dramatically and, in the worst case, becomes a fire risk.
The C-rating is a specification to understand, not a bigger-is-always-better sticker. Size your packs around the continuous rating, respect the difference between burst and sustained current, and watch for sag and heat. Do that, and every one of your batteries will punch harder and last longer.