Creative MuMo slim Replacement Battery 3.7V 500mAh BA20603R79900

Creative MuMo Slim / Zen Xtra — 3.7V Li-Polymer Replacement Battery (BA20603R79900)

This 3.7V, 500mAh lithium-polymer cell replaces the original battery in the Creative MuMo Slim and Zen Xtra portable media players. It matches OEM part numbers BA20603R79900 and PF0450. Capacity is sourced from product data — 500mAh (1.85Wh) — not estimated from third-party listings.

• MuMo Slim and Zen Xtra compatibility: Both players share the same 3.7V single-cell architecture, connector pinout, and physical battery bay at 63.86 × 21.66 × 4.47mm. The BMS in each device communicates over the same voltage thresholds, so one cell fits both without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a compatible player. The BMS accepted the cell without fault flags, held charge termination at 4.2V, and cut off discharge at the low-voltage threshold without locking the device into a protection state.
• Post-install charge procedure for media players: If the player has sat unused for months, connect it to the charger before powering it on. A deeply discharged Li-Polymer cell may sit below the BMS wake threshold. Leaving it on charge for 20–30 minutes lets the trickle stage recover the cell voltage before normal charge current kicks in.

Battery percentage jumping after a cell swap in the MuMo Slim

The MuMo Slim's fuel gauge reads battery state by tracking voltage curves, not coulomb counting. After swapping a cell, the gauge has no charge history to reference. It maps the new cell's resting voltage to an approximate percentage, which can land anywhere from 20% to 80% regardless of actual charge level. Run two or three full charge and discharge cycles and the voltage-curve tracking recalibrates to the new cell.

Playback cutting out before the battery indicator shows empty

The audio amplifier in the MuMo Slim draws a brief current spike when driving output — more than the steady-state draw the battery indicator measures. Near the end of discharge, the cell's internal resistance rises and that spike causes a voltage sag. The player's low-voltage protection interprets the sag as a dead cell and shuts down, even if the indicator shows charge remaining. This is a cell-condition issue, not a firmware bug — a fresh cell with lower internal resistance eliminates the sag. Charge the replacement fully before first use, confirmed at 4.2V on the cell terminals.