Motorola Krave ZN4 BN61 Replacement Battery 3.7V 850mAh

Motorola Krave ZN4 / Rapture VU30 — 3.7V Li-ion Replacement Battery (BN61)

This is a 3.7V, 850mAh Li-ion cell built to replace the original BN61 / SNN5832A battery in the Motorola Krave ZN4 and Rapture VU30 clamshell phones. Both handsets share the same battery bay dimensions and connector, so one part number covers both models. Capacity is 850mAh — match the original spec, not a third-party upsized figure.

• Krave ZN4 and Rapture VU30 compatibility: Motorola used the same battery bay, connector pinout, and charge IC across both models. The BN61 fits either phone without modification — same 46.21 × 33.95 × 5.17mm footprint and the same three-contact interface the charge IC expects.
• Bench tested on actual hardware: We cycled this cell through a full discharge-charge sequence and confirmed the BMS accepted charge current without fault flags. Charge termination triggered correctly at 4.2V, and the protection circuit tripped cleanly on an over-discharge test.
• Fuel gauge recalibration on first use: After fitting a new cell, run one complete discharge down to auto-shutoff, then charge uninterrupted to 100% before normal use. The Krave ZN4 fuel gauge IC is calibrated against the old cell's discharge curve — skipping this step causes the percentage counter to jump or report full charge early.

Sudden shutdown at 20–30% on the Krave ZN4

This is a voltage cliff, not a capacity problem. Under peak load — backlight on, call active, keypad lit — the cell's internal resistance causes voltage to sag below the BMS cutoff threshold even while the fuel gauge still reads charge remaining. Older or deeply discharged cells hit this cliff earlier because their internal resistance is higher. A fresh cell at 850mAh with low internal resistance sustains voltage under load much longer, pushing that cutoff point well below 20%. If shutdowns persist after fitting the new cell, complete the fuel gauge recalibration cycle first.

Phone shows wrong battery percentage after cell swap

The Krave ZN4's fuel gauge IC stores a discharge curve profile for the cell it last learned on — the factory-fitted original. A replacement cell has a slightly different discharge curve, so the IC maps voltage readings to percentage values that no longer match reality. The fix is one full uninterrupted discharge-to-shutoff followed by a full charge to 100%. That single cycle gives the coulomb counter enough data to rewrite its reference curve against the new cell. After that cycle, percentage reporting stabilises.