ALPSAT Satfinder 3HD Replacement Battery 7.4V 3400mAh

ALPSAT Satfinder Spare Part 3HD — 7.4V Li-ion Replacement Battery (4SF3HDS1)

This is a 7.4V Li-ion replacement battery rated at 3400mAh (25.16Wh) for the ALPSAT Satfinder Spare Part 3HD portable satellite finder. The Satfinder 3HD is a handheld field instrument used by technicians to locate and align satellite signals during installation and maintenance work. When the original cell degrades and the unit can no longer hold a charge through a full job, this pack restores field-ready power.

• Satfinder 3HD platform fit: The 3HD uses a dedicated battery bay with a three-contact interface. The BMS in this pack matches the charge communication protocol the instrument expects — mismatched cells without the correct handshake trigger immediate charge rejection on the 3HD's charge circuit.
• Bench tested on actual hardware: We cycled this pack through signal-scan and transponder-lock sequences on the 3HD. The BMS held stable through the tuner's initialisation current draw and did not trip on repeated cold-start events across multiple cycles.
• First-use calibration on the 3HD: After fitting this pack, run the instrument through a full signal-scan calibration cycle before taking it to site. The 3HD maps battery state during that cycle, and skipping it causes the low-battery indicator to fire prematurely on your first real measurement session.

BMS lockout after the Satfinder 3HD sits unused in a carry case

Li-ion cells self-discharge over time. If the 3HD sits unused for several months, the pack can drop below the BMS's minimum recovery threshold — typically around 2.5V per cell. At that point the BMS enters a protective lockout state and the instrument will not power on or respond to the charger. Connecting the pack to a Li-ion compatible charger with a recovery or trickle mode can bring the cell voltage back above the wake threshold. Once the BMS sees voltage above approximately 3.0V per cell, normal charging resumes.

Satfinder 3HD display showing erratic battery percentage after a pack swap

The 3HD's fuel indicator is calibrated to the voltage curve of the original cell. A new pack with a fresh, full charge presents a slightly different resting voltage than a worn original, which causes the indicator to read inconsistently — jumping between levels or reporting low charge on a full cell. This corrects itself after one or two full discharge-and-charge cycles, during which the instrument re-anchors its percentage thresholds to the new cell's actual voltage curve. Run those cycles under normal field conditions — powering up, scanning, and locking onto a signal — rather than leaving the unit idle. After two full cycles the readout stabilises.