Calculate required battery capacity, C-rating, and weight for your target flight time and power needs.
Required Capacity
Minimum capacity for 10 min at 15A
Recommended Pack Size
Nearest common battery size
Required C-Rating
Low discharge — Li-Ion cells are ideal for this current draw.
Estimated Battery Weight
Based on LiPo energy density (150 Wh/kg)
Estimated All-Up Weight
Drone (500g) + battery (308.3g)
Battery Energy
4S × 3125mAh
The C-rating on a LiPo battery is the maximum continuous discharge rate expressed as a multiple of the pack capacity. A 2,200mAh battery rated at 45C can theoretically deliver 45 × 2.2Ah = 99A continuously. The formula is straightforward: multiply the C-rating by the capacity in amp-hours to get the maximum safe current draw.
In practice, manufacturer C-ratings are frequently exaggerated. Independent testing by groups like Lithium Battery Laboratory consistently shows real-world continuous discharge capabilities 30–60% below the printed rating on budget packs. For critical applications — particularly high-current racing and lifting applications — verify C-rating with a calibrated load tester or thrust stand measurement rather than trusting the label.
Required C-Rating
Your required C-rating equals your maximum peak current divided by the pack capacity in amp-hours. A 15A build drawing 15A from a 1,500mAh (1.5Ah) pack requires only 10C — well within any LiPo's capability. The same 15A draw from a 300mAh pack requires 50C, pushing into premium territory.
Burst vs Continuous Ratings
Many batteries list both a continuous and a burst C-rating. Burst ratings apply for very short intervals (typically 10–30 seconds). Full-throttle acrobatic sequences and race laps often demand burst-level current. Size your pack so the continuous C-rating covers your average current, not just hover current.
C-Rating and Voltage Sag
Under high load, battery voltage drops — voltage sag. A pack operated near its maximum C-rate will sag significantly, reducing effective motor RPM and ESC input voltage. This causes brownouts, arming failures, and reduced motor performance at full throttle. Sizing to a lower C-rate percentage (using a larger or higher-rated pack) reduces internal resistance heating and voltage sag.
Choosing between LiPo and Li-Ion is not simply about which is "better" — they excel in different scenarios. The critical difference is energy density versus discharge rate.
| Property | LiPo | HV LiPo | Li-Ion | LiFePO4 |
|---|---|---|---|---|
| Nominal V/cell | 3.7V | 3.85V | 3.6V | 3.2V |
| Energy density | ~150 Wh/kg | ~160 Wh/kg | ~220 Wh/kg | ~100 Wh/kg |
| Max C-rating | 45–120C | 45–100C | 5–10C | 30–50C |
| Usable depth | 80% | 80% | 85% | 90% |
| Best use case | Racing / freestyle | Sport / freestyle | Long endurance | Reliability-critical |
Li-Ion's superior energy density (~47% more Wh/kg than standard LiPo) means you can carry the same energy in a lighter pack — but only if your current demands are modest. The Samsung 21700-series cells popular in long-range builds offer ~220 Wh/kg with a maximum discharge of around 10A per cell. A 4-cell parallel arrangement (4P) can deliver 40A total — sufficient for a hovering 7" long-range quad, but nowhere near enough for a racing build that pulls 100A+ during gate passes.
LiFePO4 occupies a unique niche: lower energy density than both LiPo and Li-Ion, but exceptional cycle life (2,000–3,000 cycles vs 200–500 for LiPo), flat discharge curve, and the best thermal stability of any common chemistry. Used in commercial mapping drones and fixed-wing UAVs where longevity and safety outweigh raw energy density.
Battery pack configuration is described as nS–nP where S denotes cells connected in series and P denotes cells connected in parallel. A 4S pack has four cells in series. A 4S2P pack has two such series strings connected in parallel.
Series (S) — increases voltage
Each cell in series adds its voltage. Four 3.7V LiPo cells in series produce 14.8V nominal. Higher voltage enables motors to run at higher RPM without increasing current, reducing resistive losses. The S-count is why 6S is more efficient than 4S for the same power output.
Parallel (P) — increases capacity
Each cell string in parallel adds to total capacity and reduces effective internal resistance. A 2P pack doubles capacity (mAh) and halves the effective C-rating requirement — each string supplies half the total current. Li-Ion builds commonly use high-P configurations to compensate for low individual cell C-ratings.
Most hobby LiPo packs are 1P — a single series string. Commercial and long-endurance packs increasingly use multi-P configurations. When comparing packs, always check both S and P to understand the true cell count: a "4S2P" pack has 8 cells total, twice the capacity of a standard 4S pack, and is heavier accordingly.
LiPo batteries contain flammable electrolyte under pressure. Damage, overcharging, over-discharging, or short-circuit can cause thermal runaway — an uncontrolled exothermic reaction that produces intense heat, fire, and toxic smoke. These are not hypothetical risks; LiPo fires are the leading cause of drone-related workshop and vehicle fires.
Storage voltage
3.8V per cell (storage voltage) is the ideal long-term storage state. Most quality chargers have a dedicated storage charge/discharge mode. Storing fully charged or fully depleted degrades cell capacity significantly — expect 20–30% capacity loss within a season if stored incorrectly.
Never over-discharge
Discharging below 3.0V per cell causes irreversible copper dissolution inside the cell. Many builders use OSD voltage alerts at 3.5V/cell (per cell, not pack voltage). Land immediately when the voltage warning triggers; continuing to fly risks causing a fire on the next charge cycle.
Use LiPo-safe bags
Always charge and store LiPo batteries in a purpose-built LiPo-safe bag or metal ammunition box. These contain the fire if thermal runaway occurs. Never charge unattended, never charge in a car, and keep charged packs away from flammable materials.
Inspect before every flight
Visually inspect packs for swelling (puffing) before every flight. A puffy pack has internal gas buildup indicating chemical degradation. Puffed packs should be discharged to storage voltage, punctured in a salt-water bucket to neutralise, and disposed of per local regulations.
Adding a larger battery increases available energy but also increases the weight the motors must lift — which increases hover power demand, which in turn reduces the effective flight time gain. This creates a diminishing returns curve: each additional gram of battery returns progressively less flight time.
The trade-off can be modelled as follows. If a drone weighs W grams without battery and we add a battery of mass M grams, the new hover power is proportional to (W + M)^(3/2). If battery mass doubles, power demand grows by 2^(3/2) ≈ 2.83× — requiring even more energy per minute to remain airborne. The sweet spot for most builds is when battery mass is 20–30% of total all-up weight.
| Drone Type | Battery % of AUW | Typical Battery |
|---|---|---|
| 5" FPV Freestyle | 25–35% | 4S 1300–1500mAh |
| 7" Long Range | 30–45% | 4S 3000–5000mAh Li-Ion |
| Cinematic / Heavy Lift | 20–30% | 6S 5000–8000mAh |
| Micro Whoop | 30–40% | 1S 300–650mAh |