Motorola I576 Replacement Battery BT90 3.7V 1800mAh

Motorola I576 / Rival A455 / ROKR Z6m — 3.7V Li-ion Replacement Battery (BT90 / SNN5826A)

This 3.7V Li-ion battery replaces OEM part numbers BT90, SNN5826A, SNN5759, and SNN5765 across several Motorola handsets. It fits the I576, Rival A455, Z6tv, and ROKR Z6m, among others. Capacity is 1800mAh (6.66Wh), matching the original cell specification.

• Cross-model fit — I576, Rival A455, Z6tv, ROKR Z6m: These handsets share the same battery bay dimensions (53.60 × 35.40 × 9.60mm), connector pinout, and 3.7V nominal voltage rail. The BMS handshake protocol is identical across the group, so one cell replaces stock across all listed variants without modification.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on the I576 platform. The BMS accepted the charge handshake on the first connection, held the 3.7V nominal rail under screen-on load, and tripped the protection circuit correctly at the low-voltage cutoff threshold.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one complete discharge-charge cycle before resuming normal use. This lets the fuel gauge IC map its coulomb counter against the new cell's actual discharge curve — skipping this step is the main reason percentage readings appear inaccurate after a cell swap.

Sudden shutdown at 20–30% on the Motorola I576 after a cell swap

This happens because the fuel gauge IC is still running a calibration curve built around the old, degraded cell. A fresh 1800mAh cell has a steeper voltage cliff under modem or display load than the worn cell the device was calibrated against. When current draw spikes — during a call, GPS fix, or screen wake — the cell voltage drops momentarily below the BMS cutoff threshold even though the displayed percentage says 25%. One full uninterrupted discharge-charge cycle recalibrates the coulomb counter and moves the reported cutoff point to match the new cell. After that cycle, shutdowns at partial charge typically stop.

Phone will not power on after the replacement battery sat in storage

Li-ion cells in storage self-discharge to roughly 2.5V per cell or below, which triggers BMS lockout — the protection circuit opens and the phone reads the pack as absent or completely dead. Plugging in the charger may show no response at all for the first several minutes. Leave the phone connected to a wall charger (not a USB port) for at least 20–30 minutes without attempting to power on; the charge IC needs to push a trickle current into the cell to bring it above the 2.8V re-enable threshold before the BMS will close the circuit. Once the phone vibrates or shows the charge screen, normal charging resumes.