Application of Lithium Polymer Batteries in FPV Drones

Battery Recommendations

When selecting a LiPo battery, opt for reputable brands to ensure performance and quality. For a lighter, more agile drone, choose a smaller battery pack. If flight duration is a priority over maneuverability, opt for a larger pack. Note that larger batteries provide higher currents but add slight weight, requiring a trade-off.

5-Inch Freestyle and Racing Drones

The most common LiPo batteries for 5-inch FPV drones (used in freestyle and racing) are 4S and 6S configurations. If you’re undecided, 6S is recommended as the industry standard in 2025. Typical capacities are around 1500mAh for 4S and 1000mAh to 1300mAh for 6S.

Are LiPo Batteries Safe?

When handled correctly, LiPo batteries are absolutely safe. However, improper use or physical damage can lead to fires. Careful handling and storing/charging in a fire-safe location are essential to minimize risks.

Understanding LiPo Battery Basics

LiPo batteries offer an exceptional power-to-weight ratio, making them ideal for FPV drones. Learning to read their labels and understanding key terms is crucial for selecting the right battery, as explained below.

LiPo Battery Voltage

LiPo batteries consist of individual cells, each designed to operate within a specific voltage range:

  • Fully charged at 4.2V per cell.

  • Fully discharged at 3.0V per cell. A “empty” LiPo doesn’t mean 0V! Discharging below 3.0V can cause irreversible performance loss or damage. Overcharging above 4.2V per cell is extremely dangerous and may cause fires.

To extend battery life, stop flying and land when the per-cell voltage reaches around 3.5V. Exceptions exist, such as with 1S Tiny Whoop batteries, where pilots may discharge to 3.2V to maximize flight time due to lower replacement costs.

Cell Count

LiPo batteries may contain multiple cells. The “S” rating indicates the number of cells connected in series, increasing the total voltage. Each cell has a nominal voltage of 3.7V, so you might see:

  • 1S = 1 cell = 3.7V

  • 2S = 2 cells = 7.4V

  • 3S = 3 cells = 11.1V

  • 4S = 4 cells = 14.8V

  • 5S = 5 cells = 18.5V

  • 6S = 6 cells = 22.2V

For example:

  • A 4S battery has a nominal voltage of 14.8V (4 × 3.7V), a minimum of 12.0V, and a maximum of 16.8V (4 × 4.2V).

  • A 6S battery has a nominal voltage of 22.2V, a minimum of 18.0V, and a maximum of 25.2V.

Higher cell counts increase motor RPM and drone power (if supported), but they are heavier and more expensive.

Fun Fact: Connecting two identical batteries in series doubles the voltage but keeps capacity the same (e.g., two 2S 1000mAh batteries in series become one 4S 1000mAh). In parallel, capacity doubles while voltage remains the same (e.g., one 2S 2000mAh pack). Labels may include “P” (e.g., 4S2P or 6S2P), where “P” indicates parallel groups. 6S1P means 6 cells in series, 1 group in parallel (often omitted as “1P” is standard), while 6S2P means 6 cells in series, 2 groups in parallel (totaling 12 cells).

Capacity

Capacity, measured in mAh (milliamp-hours), indicates the current a battery can deliver continuously for one hour until depleted. (1000mAh = 1Ah.) For a 1300mAh (1.3Ah) LiPo:

  • At 1.3A, it lasts one hour.

  • At 2.6A, it lasts 30 minutes.

  • At 39A, it lasts 2 minutes (1.3/39 = 1/30 hour).

Higher capacity extends flight time but increases weight and size. Balancing capacity and weight is key to optimizing flight efficiency and performance.

C Rating

The C rating indicates the maximum safe current draw without damage, calculated as:

  • Maximum current = Capacity × C rating.

Exceeding this can overheat the battery, increase internal resistance over time, shorten lifespan, or cause thermal runaway (fire). Higher C-rated batteries (even with the same capacity) are often heavier. They excel in high-power drones but may be overkill for low-power cruisers, where added weight could reduce flight time. C ratings are useful within the same brand but can be exaggerated for marketing, so rely on recommendations over comparisons.

Internal Resistance (IR)

All electronics, including batteries, have resistance. Battery internal resistance (IR) measures opposition to current flow. Lower IR means more efficient power delivery for FPV drones. Monitoring IR helps assess battery health and determine replacement timing, as it naturally increases with use and age. Poor practices like over-discharging, overcharging, high-current draws, or overheating accelerate aging.

High IR causes voltage sag (drops under load), reducing motor RPM, power, and responsiveness. Batteries designed for low-current applications (e.g., radios or FPV goggles) have higher IR, as do 18650 Li-ion batteries compared to typical LiPos.

Battery Connectors

All LiPo batteries (except 1S) have two connectors: a main discharge connector and a balance connector. The discharge lead (thicker red and black wires) powers the drone. The balance lead (thin wires to a white connector) monitors cell voltages, with wire count matching cell count plus one:

  • 2S = 3 wires

  • 3S = 4 wires

  • 4S = 5 wires

  • 5S = 6 wires

  • 6S = 7 wires

Common discharge connectors include XT60 (for 5-inch+ drones) and XT30 (for smaller drones), differing in size and current rating. Balance connectors (JST-XH) connect to the charger for voltage balancing during charging.

Dead Cells

If a cell shows no voltage during checks, it may be dead. Use a multimeter to confirm—avoid using a failed battery.

How Many Packs for Beginners?

Start with 4 battery packs for FPV flying, offering 40 minutes of flight time (5-10 minutes per flight, including setup and crashes). Charging in the field can extend this further.

Weight

Battery weight should be about half the drone’s dry weight (without battery or GoPro). For a 600g drone, a 300g battery suits agile freestyle flying. For cinematic or slow flight, a 1:1 ratio may work. Larger batteries maximize flight time for long-range or cinematic drones where power and responsiveness are less critical.

Determining Drone Current Draw

After selecting motor and propeller sizes, check thrust data and current draw (e.g., a motor with a 5040×3 propeller at full throttle draws 36.74A). For a quad with four motors, total max draw is 36.74 × 4 = 146.96A. Reduce this by 30-40% for real-world use (e.g., 40-60% throttle, lower current due to airflow), ignoring minor draws from other components.

Choosing the Best Battery Capacity

Match capacity to drone size and C rating. General guidelines for freestyle/racing drones:

  • 4S LiPo: 7″ (1500-2200mAh), 5″ (1300-1800mAh), 4″ (850-1300mAh), 3″ (650-1000mAh)

  • 6S LiPo: 7″ (1200-1500mAh), 5″ (900-1300mAh), 4″ (550-900mAh), 3″ (400-650mAh)

Calculate C rating: C rating = Current draw / Capacity. A good rule is a battery weight half the drone’s weight, though this may vary by configuration.

Charging Speed: How Fast Should You Charge?

Charge at 1C or lower to minimize stress (e.g., 1.5A for a 1500mAh battery, 0.9A for a 900mAh battery), taking about one hour. Some batteries support 3C or 5C fast charging—verify specs before use, as higher rates risk overheating or fires. Stop charging if the battery feels hot, indicating over-speed or a defect.

When to Land

Land when battery voltage reaches 3.5V to 3.6V per cell. Flying lower stresses the battery, reducing lifespan, as cells heat up and degrade. Voltage drops faster below 3.5V, risking over-discharge before safe landing. Keeping it above 3.5V minimizes cell imbalance and damage.