Motorola V878 Replacement Battery SNN5734A 3.7V 750mAh

Motorola V878 — 3.7V Li-ion Replacement Battery (SNN5734A)

This is a 3.7V, 750mAh Li-ion replacement battery for the Motorola V878 flip phone. It slots into the original battery bay and restores power to calling, texting, and onboard applications. Capacity is 750mAh (2.78Wh) — matching the original cell specification.

• V878 compatibility: The V878 uses a single-cell 3.7V Li-ion pack with a three-contact connector carrying voltage, ground, and a BSI (Battery Size Indicator) sense line. This battery carries the correct BSI resistor value so the phone's power management IC recognises it and does not throw a "battery not supported" warning.
• Bench tested on actual hardware: We ran charge and discharge cycles through the V878's onboard charge IC and confirmed the BMS protection circuit trips correctly on overcharge and low-voltage cutoff without false disconnects mid-cycle.
• Fuel gauge recalibration on first install: After fitting this battery, run one full discharge to auto-off followed by a complete charge before using the phone normally. The V878's fuel gauge IC is calibrated against the old cell's discharge curve — one full cycle resets the reference point so the percentage readout tracks accurately.

Why the V878 reports wrong battery percentage after a cell swap

The V878 uses a fuel gauge IC that tracks capacity by measuring voltage against a stored discharge curve from the original cell. A new cell has a slightly different internal impedance profile, so the IC's reference no longer matches the actual charge state. The phone reads the voltage correctly but maps it to the wrong percentage on the old curve. One full discharge-to-cutoff and full recharge gives the IC a new reference point and corrects the drift.

Sudden shutdown at 20–30% remaining on the V878

This happens when the cell voltage drops sharply under load — a call or backlight burst draws enough current to push voltage below the BMS cutoff threshold even though the display still shows charge remaining. On an aged original cell it means the cell is worn; on a freshly installed replacement it usually means the fuel gauge IC has not yet recalibrated and is misreporting state of charge. Run one full discharge-charge cycle first. If shutdowns continue, check that the BSI contact pin on the battery bay is clean and making firm contact — a dirty pin raises apparent internal resistance and triggers an early cutoff.