7.3 Battery Types, Specifications and Dangerous Goods

The Five Energy Sources Schedule 4 Names

Most RPA candidates only ever handle lithium polymer packs, but the syllabus asks about five chemistries and expects you to know why LiPo won.

A related chemistry worth knowing is lithium-ion (Li-ion), used in "smart battery" packs on many commercial airframes. It has higher energy density than LiPo per unit mass but a lower maximum discharge rate, so it suits endurance-focused aircraft rather than high-thrust ones.

Decoding a Pack Label

A typical label reads something like: 6S1P 22.2 V 16,000 mAh 15C / 30C burst.

Series and parallel

• Series (S): voltage adds, capacity stays the same. Two 3S 5,000 mAh packs in series give 6S 5,000 mAh.
• Parallel (P): capacity adds, voltage stays the same. Two 3S 5,000 mAh packs in parallel give 3S 10,000 mAh.

Both increase the total energy stored, but they do so in different ways. Series raises the voltage the motors see, which raises rpm for a given Kv. Parallel raises the current the pack can supply and the run time, without changing rpm. Substituting a 6S pack into an airframe designed for 4S can destroy ESCs rated for the lower voltage — always check the cell count, not just the physical fit.

The Two Plugs

Every multi-cell RPA pack has two connectors and Schedule 4 names both:

• The main power plug — the heavy connector (XT60, XT90, AS150, EC5 and similar) carrying the full discharge current to the aircraft.
• The balance plug — a small multi-pin connector with one wire per cell junction, letting a charger or cell checker read and equalise each cell individually.

The balance plug is the safety-critical one. Without it, a charger can only see total pack voltage; a pack reading a healthy 25.2 V could contain one cell at 4.4 V (over-charged, a fire risk) and another at 4.0 V, and the charger would never know. Always charge through the balance lead, and always check individual cell voltages before flight.

State of Charge and Cell Health

Cell voltage is the practical proxy for state of charge on a LiPo:

A cell checker is a small device that plugs into the balance lead and reads each cell. It is the fastest pre-flight battery check there is, and the single most useful $20 item in a drone bag. The pass criterion is not just "all cells above 4.1 V" but all cells within about 0.05 V of each other. A pack with one cell 0.1 V or more adrift is unbalanced or has an internal fault and should be grounded.

Beyond voltage, serviceability is judged by:

• Physical condition — any swelling, puffiness, or a soft spot means retire the pack immediately.
• Internal resistance, if your charger measures it. Rising internal resistance is the clearest early indicator of a pack approaching end of life, and it shows in flight as increasing voltage sag.
• Cycle count — many smart packs log this. Manufacturers typically publish a useful life of a few hundred cycles.
• Temperature after flight — a pack that is hot rather than warm has been worked beyond its comfortable current.

Batteries as Dangerous Goods

Schedule 4 topic 4(d) asks specifically about batteries classified as dangerous goods for air transportation, and this is a real operational issue for any remote pilot who flies to a job.

Lithium batteries are Class 9 dangerous goods. The governing measure is watt-hours (Wh):

$\text{Wh} = \text{Voltage (V)} \times \text{Capacity (Ah)}$

Worked example. A 6S 16,000 mAh pack is 22.2 V × 16 Ah = 355 Wh — far above the limits most airlines apply to passenger carriage, and typically requiring freight arrangements as declared dangerous goods. A 4S 5,000 mAh pack is 14.8 × 5 = 74 Wh, which falls in the band that many airlines permit in carry-on baggage with prior approval.

The rules that apply almost universally:

• Carry-on only. Spare lithium batteries must travel in the cabin, never in checked baggage, because a fire in the hold cannot be fought.
• Terminal protection. Tape the terminals or carry each pack in its own bag or fire-resistant pouch so nothing can short across them.
• Quantity limits and approval thresholds vary by airline and by watt-hour band. Check with the specific carrier before you travel.
• Charge state. Many carriers require spares to be transported at or near storage charge rather than fully charged.

Road transport within Australia is less regulated for small quantities but the same physics applies: terminals insulated, packs in fire-resistant containers, secured so they cannot move, and out of direct sun. A pack left on a car dashboard on a 40-degree day is a genuine fire risk, and it is also a pack you should retire afterwards even if it looks intact.