About this replacement
NGM W13-NM8819 / Clio / Dandy / Joy — 3.7V Li-ion Replacement Battery (BL-OS4)
This is a 3.7V Li-ion cell rated at 1000mAh (3.7Wh), built to the BL-OS4 specification. It fits the NGM W13-NM8819 and a range of related NGM handsets including the Clio, Dandy, and Joy. If your original cell no longer holds a charge or the phone shuts down unexpectedly, this is the direct swap.
- W13-NM8819 / Clio / Dandy / Joy platform fit: These NGM handsets share the same battery bay dimensions (53.55 × 34.00 × 5.40mm), connector pinout, and BMS handshake protocol — which is why a single BL-OS4 cell covers the whole range without modification.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on NGM hardware. The BMS accepted the cell without fault flags, charge termination triggered cleanly at 4.2V, and the protection circuit tripped correctly at the low-voltage threshold.
- Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging begins — without this step, the percentage readout will drift and early shutdowns are common.
Sudden shutdown at 20–30% on the replacement cell
A new BL-OS4 cell has a slightly different internal resistance profile than the worn cell it replaces. Under high-draw moments — modem transmit bursts, screen-on wake — the voltage can sag below the BMS cutoff threshold even when the fuel gauge still reads 20–30%. The fuel gauge IC was calibrated against the old cell's curve, so it misreads the remaining capacity. One full discharge-to-shutdown followed by a full charge corrects the calibration. After that cycle, shutdowns at partial charge should stop.
Phone not powering on after the battery sat in storage
Li-ion cells shipped or stored for extended periods can drop below 2.5V per cell. At that point the BMS latches into lockout mode and refuses to pass current — the phone shows nothing when you press the power button. Connect the phone to a charger and leave it for 15–20 minutes without pressing anything. The charge IC trickle-charges the cell back above the BMS re-enable threshold, typically around 2.9V, at which point normal charging resumes. If the charging indicator still does not appear after 30 minutes, check that the charger output is stable at 5V.