About this replacement
HPRT A300S / A300L — 7.4V Li-ion Replacement Battery (KM310BU)
This is a 7.4V, 1500mAh Li-ion replacement battery for the HPRT A300S and A300L portable thermal printers. It slots in where the original KM310BU battery sits and restores full cordless printing capability. The cell matches the OEM voltage and capacity so the printer's BMS recognises the pack without errors.
- A300S and A300L compatibility: Both models share the same battery bay, connector pinout, and 7.4V BMS handshake. One pack covers either unit — no firmware differences affect how the BMS reads the cell.
- Bench tested on actual hardware: We ran this pack through charge, discharge, and reconnect cycles on the A300S. The BMS accepted the cell on first connect, reported charge state correctly through the printer's status display, and the paper feed motor pulled full torque at load without tripping protection.
- Post-install print sequence: After fitting this battery, charge it fully, then run five test prints before deploying the unit in the field. The paper feed motor draws a brief high-current pulse on each feed cycle — running a short print sequence confirms the BMS current profile has settled correctly for the new cell.
Why the A300S stops printing after sitting unused for weeks
Thermal printers like the A300S draw very little standby current, which means a degraded or partially discharged battery can drop below the printer's minimum drive voltage without any obvious warning. The paper feed motor and thermal head both require a stable 7.4V rail — if the cell falls below roughly 6.8V, the printer may power on but refuse to execute a print job. A full charge cycle before use is the fix. If the pack won't accept a charge after long storage, the BMS may have entered deep-discharge lockout and needs a slow pre-charge from the dock before normal charging resumes.
Bluetooth dropping mid-print job on the A300S
The A300S radio stack and print engine share the same battery rail. When the cell voltage sags under the combined load of a print job and active Bluetooth, the radio is the first subsystem the firmware sheds to protect the motor drive. This shows up as a mid-job disconnect rather than a print failure. It happens most often with an aged cell that can no longer hold voltage under load — not a pairing issue. Fit a fresh battery, charge to 100%, and confirm the printer's status indicator reads full before sending a multi-page job.