Drone battery history: what flight logs can and can't tell you

Observed history is not the full lifecycle

A log only covers the time the battery was in a flying aircraft. Charging, storage temperature, long periods at full charge, transport and any flights whose logs you never imported are all invisible. A battery history built from logs is an observed history: a partial view, however carefully it's assembled.

BMS full-charge capacity is the battery's own estimate

Smart batteries report a full-charge capacity calculated by their battery management system (BMS). It's worth tracking, but it is the pack's estimate of itself — not an independent measurement and not a health certificate. Different firmware can calculate it differently.

Cycle counts are cumulative — read them, never add them up

The cycle count in a log is the BMS's running total at the time of the flight. Summing it across flights produces nonsense. The right value is the latest reading you have, along with the date it was observed.

Missing is not zero

If a log has no cell voltages or temperatures, the value is unknown, not zero. Averaging a missing value as 0 makes the battery look worse (or better) than it is. Keep gaps visible and count how many flights actually contributed to each figure.

Compare like with like

Before comparing two batteries, or one battery against its own past, check that the flights are comparable:

• Same battery model and cell count.
• Similar temperature — cold packs sag more under load.
• Similar state-of-charge window — a pack behaves differently at 90% than at 30%.
• Similar load — a hover and a fast transit are not the same test.

Flymetry only shows a comparison when these conditions hold. A capacity trend needs at least three matched dates and at least three comparable pairs; a load benchmark needs enough coverage and samples. Otherwise it explains why there isn't enough data instead of drawing a line anyway.

No health scores, no arbitrary thresholds

Flight-log data does not yield a true internal-resistance measurement, a remaining-life prediction or a fit-to-fly verdict, and Flymetry provides none of these. We also don't publish replacement thresholds like "retire at X cycles" — that belongs to the manufacturer's guidance and your own operations manual. Healthy-looking data does not mean a battery is fit to fly.

A practical routine

1. Import every flight log, including short ones, so the observed history has fewer holes.
2. Label physical packs with their serial number so logs and hardware match.
3. Note the latest cycle count and BMS capacity per pack, with dates.
4. Look at cell spread at the end of comparable flights, not single outliers.
5. Escalate anything unusual to your maintenance routine and the manufacturer's guidance.

Sources

• Flymetry's battery analysis rules as implemented in the current MVP (conditional comparisons, missing values kept as null).
• Your battery manufacturer's documentation for storage, charging and retirement guidance.