About this replacement
Amazon Kindle Fire HDX — 3.8V Li-Polymer Replacement Battery (S12-T1-S)
This 3.8V, 4550mAh lithium-polymer battery replaces the original cell in the Amazon Kindle Fire HDX and Kindle Fire HDX 7 (model C9R6QM). It restores power to the display, processor, and wireless radios when the factory battery no longer holds a charge. Dimensions are 125.40 × 68.20 × 4.00mm — measure your original before installing.
- HDX 7 and C9R6QM compatibility: These models share the same battery bay geometry, connector pinout, and charge IC handshake protocol, which is why OEM part numbers S12-T1-S, S12-T1, and 58-000043 all cross-reference to a single cell specification.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the Kindle Fire HDX platform. The BMS accepted the charge IC handshake without error flags, and voltage held stable under combined display and WiFi load.
- Fuel gauge recalibration after swap: After installing this battery, run the tablet down to automatic shutoff, then charge uninterrupted to 100%. This forces the fuel gauge IC to recalibrate against the new cell and clears the inaccurate percentage readings that typically appear after a battery replacement.
Kindle Fire HDX shutting down between 15% and 25% remaining
This is a voltage cliff problem, not a capacity problem. When the display brightness is high and WiFi is active simultaneously, combined current draw pulls cell voltage below the BMS cutoff threshold before the fuel gauge reaches 0%. The tablet reads 15–25% but the cell voltage has already dropped to roughly 3.2V under load. One full recalibration cycle — drain to shutoff, full uninterrupted charge — tightens the fuel gauge mapping and moves the cutoff trigger closer to the actual empty point.
Fast charging not available after battery replacement on the HDX
The Kindle Fire HDX charge controller requires at least one complete accepted charge cycle before it negotiates higher current draw with the charger. Immediately after a swap, the charge IC defaults to a conservative current profile while it characterises the new cell. Use the original Amazon power adapter — third-party adapters that don't send the correct voltage handshake will keep the device in slow-charge mode indefinitely. Complete one full charge to 100% with the OEM adapter and fast charging behaviour returns.