7.2 Batteries, LiPo Safety & TDG

7.2 Batteries, LiPo Safety & TDG

Quick Answer: LiPo packs power most small/medium electric RPAS and can catch fire if abused. Master Ah/Wh, cell voltage, C-rating, series/parallel, storage voltage, and charge discipline. Plan around voltage sag under load, not marketing flight times. Move batteries under Transportation of Dangerous Goods (TDG) rules, and design charging areas that contain heat and fire at the job site.

Batteries are both the fuel tank and a primary hazard source for electric RPAS. TP 15263 systems knowledge and real Advanced operations converge here: a pilot who cannot manage LiPo safety is a liability to clients, bystanders, and carriers.

LiPo types and energy basics

Lithium polymer (LiPo) cells use a lithium-based chemistry in a pouch (or sometimes hard-case) format common in RC and drone use. Related chemistries (Li-ion cylindrical, LiHV “high voltage” LiPo, smart drone packs with internal management) appear on commercial platforms. Exam and field principles transfer:

• High specific energy (Wh/kg) → long flights for weight, but energetic failures
• Relatively flat discharge then sharp drop near empty → easy to over-discharge if you chase “one more pass”
• Sensitive to overcharge, over-discharge, high temperature, mechanical damage, and internal shorts

Capacity, energy, and voltage

Watt-hours: Wh ≈ V_nominal × Ah. Example teaching calc: 6S 5000 mAh (5 Ah) nominal ~22.2 V → ~111 Wh. Wh matters for airline/TDG thresholds and for comparing packs of different cell counts.

Series and parallel

• Series (S): voltages add, capacity (Ah) stays the same as one cell group. 6S = six cells in series → higher system voltage, lower current for same power (P = V × I).
• Parallel (P): capacities add, voltage stays the same as one series string. 2P doubles Ah if cells match.
• Pack label 6S2P means six in series, two parallel groups—higher voltage and higher capacity.

Never series/parallel mismatched packs (different age, capacity, or cell count) with improvised wiring. Commercial dual-battery aircraft use designed harnesses and isolation logic.

C-rating (charge and discharge)

C-rating expresses current relative to capacity.

• 1C discharge on a 5 Ah pack ≈ 5 A continuous (theoretical rating basis).
• A pack marked 20C continuous on 5 Ah suggests up to ~100 A continuous if the rating is honest—treat marketing C-ratings skeptically; heat and sag tell the truth.
• Charge rates are often 0.5C–1C unless the manufacturer and charger explicitly support faster charge. Faster charge increases heat and stress.

Multirotor hover and climb can demand high burst current. Undersized packs or aged high-resistance packs show voltage sag, ESC low-voltage events, and swollen cells over time.

Hazards: swelling, fire, thermal runaway

Warning signs

Thermal runaway (concept)

Thermal runaway is a self-reinforcing temperature rise: heat increases internal reactions, which produce more heat, often ending in fire and reinition of adjacent cells. Once a LiPo fire starts, ordinary extinguishers may not “turn off” the chemistry; priorities are life safety, isolation, and preventing spread. Many operators use sand, a LiPo bag/safe, or large amounts of water for cooling adjacent materials per local fire guidance—know your site plan before you need it.

Never leave charging packs unattended on flammable surfaces (car seats, sofas, dry grass). Prefer fire-resistant containers, hard floors, away from exits that people must use, and with a way to remove a burning pack outdoors if safe to do so.

Charge cycles, storage, and maintenance

Charging discipline

1. Use a charger and profile matched to chemistry (LiPo vs Li-ion vs LiHV) and cell count.
2. Prefer balance charging so cells stay matched; large cell voltage deltas are a red flag.
3. Set correct cell count and current; double-check before pressing start (classic 3S vs 4S mis-set fires).
4. Charge in a controlled area (see below); do not charge inside the aircraft unless the manufacturer’s smart system is designed for it and SOPs allow.
5. Do not charge damaged, wet, or swollen packs.
6. After flights, allow packs to cool before charging.

Storage and long-term care

• For multi-day storage, bring packs to storage voltage, not full 4.2 V/cell and not near empty.
• Avoid hot vehicles and direct sun; cold reduces available capacity and increases sag—warm packs gently to manufacturer-safe temperatures before high-load flight.
• Cycle logs (charge count, residual capacity estimates, IR if available) support retirement decisions.
• Physical inspection of leads, balance taps, and heat-shrink every charge session.

Discharge curves and operational energy

A LiPo under light load may show healthy voltage while the same pack under hover current sags into fail-safe territory. Practical implications:

• Plan missions with reserve for wind, DA, and go-around—not empty-tank optimism.
• Prefer current- and Wh-based telemetry when available over “% remaining” alone.
• Cold weather: expect less usable energy and more sag; keep packs insulated until launch.
• After a high-load flight, resting voltage rebounds—do not interpret rebound as “free extra capacity” for an immediate max-range sortie without thermal and sag awareness.

Transportation of Dangerous Goods (TDG)

In Canada, lithium batteries are dangerous goods when transported under many conditions. The Transportation of Dangerous Goods Act and Regulations (and related modal rules for air carriers) govern classification, documentation, packaging, marks/labels, and training for persons who handle/offer dangerous goods for transport.

What Advanced pilots should internalize

• Moving spare LiPos, smart batteries, and equipment with installed batteries is not always “just luggage.” Air travel is especially constrained (Wh limits, carry-on vs checked, airline approval, quantity limits).
• Road transport for commercial work may still trigger TDG duties depending on quantities, packaging, and whether you are transporting as dangerous goods in the course of business—know your operation’s compliance approach; do not invent exemptions from social media.
• Pack to prevent short circuits: protect terminals, prevent crushing, use non-conductive covers, separate spares from metal tools.
• Carry manufacturer ratings (Wh) and keep packs in good condition; damaged batteries face stricter movement rules and should not be casually shipped.
• Training and documentation requirements scale with the role (employee offering DG for transport vs private consumer exceptions). Commercial RPAS operators should align with company TDG procedures and Transport Canada guidance rather than informal “everyone does it” practice.

Exam framing: you will not be asked to recite every packing instruction number from memory, but you will be expected to know that lithium batteries are regulated dangerous goods, that fire/short-circuit prevention is the core packing goal, and that air carriage is tightly limited by energy content and carrier rules.

Charging-area safety for site operations

Professional site SOPs should define a battery bar:

At public events or near people (Advanced privilege space), a battery fire is an emergency management problem: smoke toxicity, crowd panic, and secondary ignition of cases/vehicles. Brief the crew on rally points and who calls emergency services.

Integrated battery go/no-go

1. Pack not swollen, not damaged, leads intact.
2. Cells balanced within manufacturer tolerance after charge.
3. Temperature in allowed range for charge and for flight.
4. Capacity/Wh and C capability match the mission (wind, DA, payload).
5. Transport to site complied with TDG/carrier rules; spares packed short-circuit-safe.
6. Charge area established before the first pack goes on the charger.
7. Reserve policy set (RTH voltage/percent that reflects loaded reality).

Bottom line: LiPo energy enables modern RPAS and causes the worst ground emergencies. Know the numbers (V, Ah, Wh, C, S/P), respect thermal runaway precursors, store and charge professionally, plan energy for sag under load, and treat TDG as real compliance—not optional paperwork—when batteries move with your Advanced operation.