Battery voltage sag

Overview

Sudden voltage drop under throttle — early low battery warning.

DJI Intelligent Battery, LiPo/LiIon FPV packs, ISDT/Q6 charger, XT30/XT60.

Symptoms

Typical "Battery voltage sag" signs in flight, app or OSD:

• Low battery warning after 2–3 min
• Throttle — voltage cliff on OSD
• Aircraft loses thrust at height
• Log cycle count and cell voltage after each flight.

Common causes

Before replacing parts, rule out software, mechanical and environmental causes:

• Old or high-cycle LiPo
• C-rating too low for current draw
• Cold battery (<15 °C)
• Corrosion on XT30/XT60 contacts

Tools needed

Prepare before diagnostics — saves time in the field:

• Multimeter
• LiPo storage bag
• Balance charger with cell readout

Step-by-step fix

Work safely: battery off when working on ESC/motors; props removed; after repair — VLOS test flight.

• Check cell IR — if uneven, replace pack.
• Use higher C-rating or larger capacity.
• Warm pack in pocket before winter flying.
• Clean contacts; check solder joints on FC.

Additional diagnostics

Log cycle count and cell voltage after each flight.

IR test on aged LiPo — uneven resistance = replace.

Cold battery — slower GPS and voltage sag.

When to contact service

If any of the following apply — do not fly and contact authorised service:

• Battery swollen, smells or smokes — dispose immediately.
• Cell below 2.5 V or short — do not charge.
• DJI BMS error after several attempts — use OEM battery.

Prevention

Prevention reduces failure risk and supports EASA Open / VLOS compliance:

• Log cycles
• Land at 3.5 V/cell minimum

Preguntas frecuentes

Is it safe to fly with "Battery voltage sag"?

No if the fault affects navigation, power, ESC or link. Fix on the ground first, then conduct a VLOS test flight in open area.

How long does diagnosis take?

Most “Battery voltage sag” cases — 15–45 min on the ground. Complex ones (firmware, hardware) may need 1–2 h and service.

Must I register repair with the NAA?

No mandatory repair registration, but a maintenance log is recommended for commercial operations.