Battery (LiPo / Li-Ion)

🟢 Start — zero knowledge, plain words. 🟡 Hands-on — building or buying, specifics and tradeoffs. 🔴 Specialist — the physics and math behind it.

🟢 Start. The battery is the fuel tank. Read 6S 1300 mAh 100C as: 6 cells in series (nominal voltage 6×3.7 = 22.2 V; full 25.2 V), 1300 mAh capacity, a claimed 100C current rating. Freestyle today flies mostly on 6S; older/cheaper setups on 4S (14.8 V). LiPos are powerful and… touchy: land at ~3.5 V/cell, store at ~3.8 V/cell, charge supervised, keep them in a fireproof bag.

🟡 Hands-on. Max current from the C-rating: $I_{max} = C \times \text{Ah}$ (100C × 1.3 Ah = 130 A — on paper; manufacturers exaggerate, so measure sag instead). Under load the voltage drops by $\Delta V = I\,R_{int}$: a pack with 16 mΩ at 100 A loses 1.6 V — that's the OSD dip at full throttle, and why worn packs "feel weak" at identical charge. Li-Ion (18650/21700) stores ~1.5–2× more energy per kilogram but delivers little current — the king of long range, banned from freestyle. The discharge curve explains why pilots watch volts, not percent:

A long flat middle and a cliff at the end: below ~3.6 V the voltage collapses fast — which is why alarms are set with margin.

🔴 Specialist. What flies is energy, not capacity: $E = V_{nom}\cdot \text{Ah}$ (6S 1300 mAh ≈ 28.9 Wh). Flight time: $t \approx 0.8E/P_{avg}$ — at an average 250 W of freestyle that's ~5.5 min; the same math explains 30–40 min from 7″ Li-Ion cruisers. 6S versus 4S at equal power means less current ($P = VI$): cooler ESCs, thinner wires, lower $I^2R$ losses. Measure pack health by internal resistance — it grows with age, deep discharges and heat. Design the power tree deliberately:

⚠️ Common mistakes: no failsafe test before the first flight; discharging "to the cliff"; charging unattended; storing packs full for weeks (they puff and lose capacity).

🖼️ Photos: your own pack lineup with markings explained; an OSD screenshot showing RSSI/LQ and voltage under load.