AeroFlex 3500A 11.1V Replacement Battery 7020-0012-500

AeroFlex 3500A / IFR 6000 / Cobham AvComm 8800S — 11.1V Li-ion Replacement Battery (7020-0012-500)

This is an 11.1V 10200mAh (113.22Wh) lithium-ion replacement battery for the AeroFlex 3500A and compatible avionics test and measurement instruments. It fits the Cobham AvComm 8800S, IFR 6000, IFR 3550R, and two additional models sharing the same connector and BMS protocol. Voltage and capacity match the OEM specification (7020-0012-500) exactly.

• AeroFlex 3500A / IFR / Cobham platform fit: These instruments share a common 11.1V three-cell architecture with a matched BMS handshake on the multi-pin connector. A pack that doesn't satisfy the handshake will trigger a battery fault before the boot sequence completes — this pack clears that check on all listed models.
• Bench tested on actual hardware: We cycled this pack through the 3500A's probe initialisation sequence, which pulls a sharp current spike as RF modules power up. The BMS held the rail without tripping cutoff, and cell voltage recovered to within 30mV across all three cells after the surge.
• Post-install calibration step: After fitting this pack, run a full calibration cycle through the instrument's system menu before field deployment. The 3500A maps battery state during calibration — skip this and the low-battery warning will trigger incorrectly on the first measurement session, interrupting logging at full charge.

BMS lockout after the instrument sat unused in a carry case for months

Li-ion cells self-discharge during storage. On the 3500A platform, if pack voltage drops below approximately 9V across the three cells, the BMS enters a sleep state and the instrument will not recognise the battery at all — no fault code, just no response. A standard charger will also refuse to begin a charge cycle because the pack voltage sits below the charger's detection threshold. The recovery method is a controlled pre-charge using a bench supply set to 10.0–10.5V at 0.5A current limit until the pack wakes and begins accepting charge normally. Do not attempt to force a full charge rate into a deeply discharged pack.

Readings drifting or session data resetting mid-logging

Sustained sensor load — particularly when the 3500A is logging continuously with active RF probes — draws enough current to cause a brief voltage dropout below the instrument's operational floor. The firmware interprets this as a power event and either resets the logging session or corrupts the tail end of the dataset. This is not a firmware bug — it is a cell-impedance issue in aged or marginal packs. A fresh pack with low internal resistance holds the voltage rail steady under that sustained draw. If dropout continues with a new pack, check that the instrument firmware is current, as older versions have tighter voltage-floor tolerances that amplify the effect.