About this replacement
Cedar CT8 / CT8X2 — 3.8V Li-Polymer Replacement Battery (4990112)
This is a 3.8V, 7500mAh lithium-polymer battery for the Cedar CT8 and CT8X2 automotive diagnostic scanners. It replaces OEM part number 4990112. Fits technicians running full-day shop sessions where the original cell no longer holds a working charge.
- CT8 and CT8X2 compatibility: Both models use the same 4990112 cell, share the same 3.8V power rail, and use the same connector and BMS handshake. One battery covers both.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the CT8 platform. The BMS accepted the cell without fault codes, held voltage across OBD communication sessions, and did not trigger low-voltage cutoff during live data streaming.
- Export vehicle profiles before swapping: The CT8 stores saved vehicle profiles and fault code history in RAM backed by the main battery. Pull those records to USB or the Cedar app before you remove the old cell — they will not survive a full power loss.
Why the CT8 BMS rejects a new cell on first boot
A freshly shipped lithium-polymer cell typically arrives at 30–50% state of charge. The CT8 BMS checks cell voltage at power-on and will refuse to boot if it reads below the minimum threshold — usually around 3.2V per cell. This is not a faulty battery. Plug the scanner in before attempting to power it on and let it charge to at least 3.6V. Once the BMS sees voltage above threshold, it will initialise and the unit will boot normally.
Wireless link dropping mid-diagnostic session
BLE and Wi-Fi modules on the CT8 draw a short current spike when polling vehicle ECUs. When the battery is degraded, voltage sags briefly under that load and the wireless stack loses its connection. The scanner may show a timeout error or simply freeze mid-read. This symptom appears before the battery indicator shows critical — the display driver voltage holds up longer than the RF circuitry. A fresh cell at full charge eliminates the sag and keeps the link stable through full OBD sessions.