About this replacement
Sepura STP8X Series — 7.4V Li-ion Replacement Battery (300-00910)
This 7.4V 1800mAh Li-ion battery replaces the OEM pack on the Sepura STP8X and STP8X000 portable digital radios. These are TETRA handhelds used across emergency services, security, and public safety operations. Voltage and cell count match the original spec exactly.
- STP8X and STP8X000 platform fit: Both variants run the same 7.4V two-cell architecture with an identical connector housing and BMS handshake protocol — one replacement battery covers both model suffixes without modification.
- Bench tested on actual hardware: We cycled this pack through the STP8X charge dock and monitored BMS response during simulated PTT transmit bursts. The protection circuit handled peak transmit current draw without tripping into lockout, and charge acceptance registered correctly on the first dock insertion.
- First dock insertion on the STP8X: If the charger shows a fault LED on first insertion, remove the pack, wipe the gold contact strip with a dry cloth, and reseat firmly. The STP8X dock requires a clean contact cycle to complete the BMS handshake before it will begin charging.
Why the STP8X cuts out mid-transmission on a new battery
A new Li-ion pack ships at storage voltage — typically 3.6–3.7V per cell, not full charge. When the STP8X transmits, it draws a sharp current spike. If the pack hasn't been fully charged first, that spike can pull cell voltage below the BMS undervoltage threshold, triggering an immediate cutoff. The radio goes silent, and the user assumes the battery is faulty. Charge the pack completely before first use — the dock needs to bring each cell to 4.2V before the battery can handle sustained RF output without tripping the protection circuit.
Bar indicator shows one fewer bar than expected after a full charge
The STP8X uses a voltage-threshold bar indicator, not a fuel gauge chip — it reads instantaneous cell voltage and maps it to a bar count. A new pack fresh off the charger may read slightly below the top threshold if the dock terminated charge early due to a minor contact impedance variation. Remove the battery, clean the contacts, reseat it, and run one full charge cycle again. After that cycle, the indicator should display correctly at the voltage the cells are actually holding — check that resting voltage is at or above 8.3V before concluding there is a fault.