I'm having the same issue. It's not my UAV, but I got the instructions below from someone in the industry:
Hard Reset the Vesper Smart Battery
Vesper batteries have an internal BMS that can lock out after:
- Over‑discharge
- Storage too long
- Temperature faults
- Sudden voltage drop
Reset procedure:
- Remove battery from aircraft and charger.
- Let it sit 10 minutes (discharges BMS capacitors).
- Press and hold the power button for 15 seconds.
- Release, wait 5 seconds.
- Press once to check LEDs.
If LEDs return → the BMS was in protection mode.
Check the Charger (Common Failure Point)
Vesper chargers are known to fail more often than the batteries.
Check:
- Does the charger LED turn on?
- Does it change color when battery is connected?
- Does the fan spin?
- Does the charger get warm?
If the charger stays cold and the LED never changes → charger failure is likely
Temperature Lockout
The Vesper battery will refuse to charge if:
- Below 5°C (41°F)
- Above 45°C (113°F)
If the battery feels cold or hot:
- Let it sit at room temperature for 20–30 minutes
- Try charging again
Battery Deep‑Discharge Lockout
If the battery sat too long, the voltage may fall below the BMS wake threshold.
Try this:
- Connect the battery to the charger.
- Leave it connected for at least 30 minutes, even if LEDs don’t turn on.
- Check for LED activity.
If it wakes up slowly → deep‑discharge recovery succeeded.
If it stays dead → cell voltage may be below recovery threshold
Check Battery Contacts
Vesper battery contacts can oxidize.
Do this:
- Inspect the gold contacts on the battery and aircraft.
- Clean gently with isopropyl alcohol (90%+) and a lint‑free swab.
- Ensure no debris is in the battery rails.
If the battery suddenly works after cleaning → contact oxidation was the cause
Hope that helps. If you've already fixed the issue, hopefully this will help the next person.
