Amazon Kindle Fire 7 2nd Gen 26S1028 Replacement Battery 3.8V 3750mAh

Amazon Kindle Fire 7 2nd Gen — 3.8V Li-Polymer Replacement Battery (26S1028)

This 3.8V, 3750mAh lithium-polymer cell replaces the original battery in the Amazon Kindle Fire 7 2nd generation tablet (model P8AT8Z). It matches the OEM part numbers 26S1028, ST40, and 58-000444. Use this when your Fire 7 no longer holds a charge, shuts down unexpectedly, or swells at the back panel.

• Fire 7 2nd Gen (P8AT8Z) fitment: This battery fits the P8AT8Z board layout. The connector pinout and BMS handshake match the original charge IC, so the tablet recognises the cell and begins charging without throwing a fault code.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the P8AT8Z board. The BMS balanced correctly, charge IC accepted the cell without a fault, and voltage held steady across a combined display and WiFi load.
• Fuel gauge recalibration after install: After fitting this battery, run the tablet down to automatic shutoff, then charge uninterrupted to 100% before use. The Fire 7 fuel gauge IC calibrates against the original cell's curve — one full cycle resets it to the new cell and clears inaccurate percentage readings.

Kindle Fire 7 shutting down at 15–25% remaining after a battery swap

The Fire 7's fuel gauge IC stores a learned discharge curve from the original cell. A new cell has a different internal resistance profile, so the IC misjudges the remaining capacity and triggers shutdown before the cell is actually depleted. This shows up most aggressively when the display is at full brightness and WiFi is active simultaneously — the combined load causes a brief voltage sag the IC reads as critically low. One full discharge-to-shutoff cycle followed by an uninterrupted charge to 100% forces the IC to re-learn the curve against the new cell.

Fire 7 percentage dropping faster than expected from a full charge

This is fuel gauge drift, not a cell fault. The charge IC on the P8AT8Z board tracks capacity using coulomb counting referenced to the old cell's baseline — after a swap, that baseline is wrong. The percentage display falls quickly from 100% because the IC has not yet mapped the new cell's actual capacity window. Run one complete discharge to automatic shutoff, then charge uninterrupted to 100% at the standard 5V input, and the drift corrects itself within that single cycle.