Sendo M500 Replacement Battery 3.7V 680mAh Li-ion

Sendo M500 Series — 3.7V Li-ion Replacement Battery (8D48-0MA10-22010)

This is a 3.7V, 680mAh Li-ion battery for the Sendo M500, M525, M550, and M551 smartphones. It replaces OEM part number 8D48-0MA10-22010. The cell slots into the original battery bay and connects to the phone's charge circuit without modification.

• M500 series fit: The M500, M525, M550, and M551 share the same battery bay dimensions and connector pinout, which is why one part number covers all four. The BMS communicates charge state over the same two-wire interface across each variant.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the bench and confirmed the BMS accepted charge handshake correctly. Charge termination triggered at the expected voltage ceiling with no false cutoff events.
• Fuel gauge recalibration on first use: After fitting this battery, disable any fast-charge adapter and run one full discharge-to-charge cycle before resuming normal use. This allows the fuel gauge IC to build an accurate discharge curve against the new cell before high-current charging begins on an uncalibrated state-of-charge map.

Sudden shutdown at 20–30% on the Sendo M500

This is a voltage cliff issue, not a capacity fault. Under peak modem or screen load, the cell voltage drops faster than the fuel gauge IC predicts, crossing the low-voltage cutoff threshold before the displayed percentage reaches zero. The phone shuts off to protect the cell. One full discharge-charge cycle recalibrates the coulomb counter and narrows the gap between the displayed percentage and actual cell voltage.

Phone won't power on after the battery sat discharged in storage

If a Li-ion cell drops below roughly 2.5V per cell during extended storage, the BMS enters lockout to prevent unsafe charging of a deeply discharged cell. The phone will not respond to the power button or show any charge indicator at first. Leave the phone connected to a low-current charger for 20–30 minutes — the BMS recovery circuit will trickle current into the cell until voltage rises above the lockout threshold, at which point normal charging resumes. Confirm recovery by watching for the charge indicator to appear, typically once the cell reaches 3.0V.