How to keep a LiPo battery log
By the BeaconUAV team. Updated
Give every pack a number, then record its cycles, its per-cell internal resistance every so often, and its health. One reading is just a number; the trend across cycles is what tells you a pack is wearing out.
Number your packs
A battery log starts with telling packs apart. Write a number on each pack and use it every time you log a flight. Without that, a set of six identical packs is one blurred history.
What to record for each pack
| Record | How often | Why |
|---|---|---|
| Cycles | Every flight (from the packs you log) | Wear accumulates per cycle, not per month. |
| Per-cell internal resistance (mΩ) | Every 10 to 20 cycles, at a similar temperature | The clearest early sign of aging. |
| Health or remaining capacity | When you measure it | A simple summary for retire-or-keep decisions. |
| Charge voltage | When charging | Spots a cell that will not balance. |
| Puffing, damage, crashes | When it happens | Physical damage overrides every number. |
Reading internal resistance
Internal resistance (IR) rises as a LiPo ages. Chargers report it per cell in milliohms. The absolute value depends on the pack, the charger, and the temperature, so compare a pack with itself over time, and cells with each other within the pack.
BeaconUAV only reports an IR trend when two readings are stamped with cycle counts at least 10 cycles apart. A rate calculated over two or three cycles is noise.
The thresholds BeaconUAV uses
These are the rules behind the pack verdicts in BeaconUAV's battery health panel. They are sensible defaults, not a safety standard: a puffed or damaged pack is retired whatever its numbers say.
| Signal | Watch | Replace |
|---|---|---|
| IR growth per 100 cycles | 10 mΩ or more | 25 mΩ or more |
| Stored health | Below 85% | 70% or lower |
| One cell vs the pack average | More than 10% higher (elevated) | More than 20% higher (high) |
Spot the pack doing all the work
Most pilots grab the same favorite packs. BeaconUAV flags a pack carrying 50% more than its fair share of the set's cycles. Rotating packs spreads the wear and keeps a set aging evenly.
A worked example
Example figures, not a real pack: a 6S pack reads an average of 4.0 mΩ per cell at cycle 20 and 7.5 mΩ at cycle 120. That is 3.5 mΩ over 100 cycles, well under the watch line, so it stays in rotation. If one cell read 5.0 mΩ against a 4.0 average, that cell is 25% above the pack average, which BeaconUAV grades as high whatever the trend says.
Key takeaways
- Number every pack and log which packs you fly.
- Take per-cell IR readings every 10 to 20 cycles, at a similar temperature.
- Judge the trend and the weakest cell, not a single reading.