AeroFlex 3500A 11.1V Replacement Battery 7800mAh Li-ion

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

This is an 11.1V, 7800mAh lithium-ion battery built to replace OEM part 7020-0012-500. It fits the AeroFlex 3500A, Cobham AvComm 8800S, IFR 6000, and IFR 3550R portable field test instruments. These units run avionics and communications test routines in the field, often far from any charging source.

• Multi-platform fit — 3500A, 8800S, IFR 6000, IFR 3550R: These instruments share the same 11.1V three-cell architecture, connector pinout, and BMS communication protocol — which is why one pack covers all four platforms without modification.
• Bench tested on actual hardware: We cycled this pack through instrument power-on, probe module initialisation, and sustained RF signal generation load. The BMS held voltage above the cutoff threshold through all three phases and reported state-of-charge correctly to the instrument's display.
• Calibration cycle before first field deployment: After fitting this pack, run a full calibration cycle through the instrument's system menu before heading out. The instrument maps battery state during that routine — skip it and the low-battery warning triggers early on your first measurement session.

BMS cutoff when a probe or test module initialises

When the 3500A or IFR 6000 powers up a connected probe or RF module, the initialisation sequence pulls a short high-current spike — often 3–5× the steady-state draw. An aged or deeply discharged pack can't sustain that spike without the cell voltage dipping below the BMS protection threshold, which triggers an immediate cutoff. This pack's cells are rated for the peak current these instruments demand at initialisation. If the instrument cuts out at exactly the moment a module connects, check that the pack is charged above 11.4V before attaching external modules.

Instrument shows inconsistent battery percentage every time it reboots

The 3500A reads battery percentage against fixed voltage thresholds stored in firmware. A new cell has a slightly different discharge curve than the worn pack it replaced, so the instrument's percentage indicator can jump around — showing 80% on one boot and 60% on the next — until the firmware recalibrates to the new pack's actual voltage profile. This settles after two or three full discharge-and-charge cycles. Run those cycles under normal instrument load, not just idle, so the calibration reflects real working conditions. After the third cycle the displayed percentage should stabilise and track consistently.