Samsung Nexus 50 Compatible Battery 3.7V 1000mAh 990208

Samsung Nexus 50 / Nexus 25 — 3.7V Li-ion Replacement Battery (990208)

This is a 3.7V, 1000mAh Li-ion replacement battery for the Samsung Nexus 50 and Nexus 25 portable digital media players. It matches OEM part numbers 990208, LKF1629ENA, and MST990208. It fits both the standard and YP-X5ZX / YP-X5X variants of these players.

• Nexus 50 and Nexus 25 compatibility: Both the Nexus 50 (YP-X5ZX) and Nexus 25 (YP-X5X) share the same 3.7V single-cell architecture, connector pinout, and BMS handshake protocol — one cell covers the full range without any modification.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a Nexus 50 unit. The BMS accepted charge current normally, voltage held steady through mid-charge, and the protection circuit tripped at the correct low-voltage cutoff without fault codes.
• First-charge behaviour after cell swap: After fitting a new cell, connect the player to its charger before powering it on. A freshly installed cell may sit below the player's minimum startup voltage, causing the device to appear dead. Letting the charger trickle into the cell for 20–30 minutes brings it above the startup threshold before you attempt to boot.

Battery percentage jumping after cell swap in the Nexus 50

The Nexus 50 reads battery level by sampling cell voltage against a fixed lookup table calibrated to the original cell. A new cell's voltage curve won't align with that table until the firmware has seen at least two or three full charge and discharge cycles. Until then, the indicator skips or jumps — this is a calibration lag, not a cell fault. Run two or three full cycles from 100% down to auto-shutdown and back to fully charged. After that, the displayed percentage tracks voltage accurately.

Playback cutting out before the battery indicator shows empty

The audio amplifier inside the Nexus 50 draws a short burst of higher current each time it drives the output stage. At the end of a cell's discharge curve — roughly below 3.5V — the cell's internal resistance rises enough that this burst causes a brief voltage sag. The BMS reads that sag as a low-voltage fault and cuts power to protect the cell, even though the indicator hasn't reached zero. If this happens consistently, charge the player fully and confirm the cell voltage reads at or above 4.1V with a multimeter at the battery terminals after a full charge.