Microtac Infinity SA9800 Replacement Battery 4.8V 700mAh

Microtac Infinity SA9800 — 4.8V Ni-MH Replacement Battery (MED585)

This is a 4.8V, 700mAh Ni-MH replacement battery for the Microtac Infinity SA9800 portable medical diagnostic instrument. Part number MED585. It restores cordless operation to the SA9800 when the original cell has lost capacity or failed entirely.

• SA9800 platform fit: The Infinity SA9800 uses a dedicated cell pack with a specific connector orientation and BMS handshake tied to the 4.8V Ni-MH chemistry. Substituting a different voltage or chemistry will cause the device to reject the battery or fail self-test on startup.
• Bench tested on actual hardware: We cycled this cell through the SA9800's charge circuit and confirmed the BMS accepted the pack, completed charge termination normally, and passed the device's power-on verification sequence without triggering a fault code.
• Post-swap startup protocol: After installing this battery, let the SA9800 complete its full power-on self-test without interruption. The BMS runs a chemistry verification step at boot. Cutting power during that window logs a false battery fault that persists until the next clean reboot.

SA9800 not completing boot sequence after battery swap

The SA9800 runs a BMS verification cycle during startup that checks cell voltage against expected Ni-MH thresholds. A new cell shipped in partial state of charge may read below the minimum threshold the device expects at boot, causing the sequence to stall or abort. This is not a fault with the cell itself — it is a charge state issue. Charge the new battery fully before the first power-on, then allow the boot sequence to run uninterrupted to completion.

Charge indicator not reaching 100% on first charge

The SA9800's charge IC applies a conservative termination threshold on cells it has not yet profiled. On the first charge cycle, the indicator may stop at 80–90% and hold there. This is the charge controller applying a reduced top-off current until it maps the cell's internal resistance. Run one complete charge-discharge cycle and the charge IC recalibrates. After that cycle, the indicator should reach full charge consistently at the expected voltage of approximately 5.5–5.6V across the pack.