Amazon Fire Phone 6581A Replacement Battery 3.8V 2400mAh

Amazon Fire Phone — 3.8V Li-Polymer Replacement Battery (26S1003-A)

This is a 3.8V, 2400mAh Li-Polymer cell that replaces OEM part 26S1003-A in the Amazon Fire Phone (model 6581A), including the 32GB and 64GB variants. It also cross-references 58-000057, 58-000068, and S12-M1-C. If the original cell no longer holds a charge or the phone shuts down unexpectedly, this is the direct swap.

• Fire Phone and 6581A tablet compatibility: Both device variants use the same physical cell format, connector pinout, and BMS handshake protocol. Voltage rail is 3.8V nominal across the board, so one cell covers the full compatibility range without hardware modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the Fire Phone platform. The BMS accepted the new cell without rejection errors, and the charge IC ramped current correctly from trickle through CC/CV phases.
• Fuel gauge recalibration on first cycle: On first use after installation, run one complete discharge down to automatic shutdown, then charge uninterrupted to 100% before using the device. This lets the coulomb counter IC map the new cell's discharge curve before normal use begins.

Sudden shutdown at 20–30% on the Fire Phone after a cell swap

A new Li-Polymer cell has a slightly different voltage-to-capacity curve than the aged cell it replaces. The Fire Phone's fuel gauge IC was calibrated to the old cell's curve, so it misreads the new cell's state of charge. When the display or modem draws peak current, cell voltage drops below the BMS cutoff threshold even though the OS reports 20–30% remaining. The fix is one full discharge-to-shutdown and uninterrupted recharge cycle — after that, the coulomb counter recalibrates to the new curve and shutdowns stop.

Fire Phone not powering on after the replacement cell sat in storage

Li-Polymer cells stored below 2.5V per cell trigger a BMS lockout — the protection circuit disconnects the cell to prevent damage, and the phone shows no response to the power button. Plug into a wall charger using the original cable, not a USB hub or PC port, and leave it for 20–30 minutes before pressing power. Most BMS circuits re-initialise once input voltage from the charger is detected above the lockout threshold. If the screen stays black after 30 minutes on charge, try a second known-good charger before assuming cell failure.