Sonim XP8 BAT-04900-01S Replacement Battery 3.8V 4850mAh

Sonim XP8 / XP8800 — 3.8V Li-Polymer Replacement Battery (BAT-04900-01S)

This 3.8V Li-Polymer battery replaces the OEM BAT-04900-01S cell inside the Sonim XP8 and XP8800 rugged smartphones. It carries 4850mAh (18.43Wh) capacity. The XP8 is a MIL-STD-810G certified device built for construction, utilities, and industrial field work — the battery sits inside a sealed chassis and handles the full current draw of the phone's LTE modem, push-to-talk radio stack, and high-brightness display.

• XP8 and XP8800 compatibility: Both models share the same sealed battery bay, connector pinout, and BMS handshake protocol. The BAT-04900-01S form factor — 86.10 × 56.14 × 7.12mm — fits the chassis without modification. Voltage rails match the phone's charge IC and power management unit exactly.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on the XP8 platform, monitoring BMS cutoff behavior under simultaneous modem and display load. The protection circuit held within expected voltage thresholds at both ends of the discharge curve.
• Fuel gauge recalibration on first use: On the first cycle after installation, disable fast charging and run one complete discharge down to auto-shutdown, then charge fully on standard current. This gives the fuel gauge IC one clean reference cycle against the new cell's discharge curve before fast charging pushes high current into an uncalibrated state.

Sudden shutdown at 20–30% on the XP8 after a cell swap

The XP8's fuel gauge IC stores a learned discharge curve from the previous cell. A new 4850mAh Li-Polymer cell has a different internal impedance profile, so the gauge misreads the remaining charge and triggers a low-voltage shutdown earlier than the percentage suggests. This is a coulomb counter calibration issue, not a fault with the replacement cell. Run one full discharge-to-shutdown and uninterrupted charge cycle with fast charging disabled. After that single cycle, the fuel gauge recalibrates to the new cell curve and the shutdowns stop.

USB-PD fast charge not activating after battery replacement

On the first charge cycle after installing a new cell, the XP8's charge IC may not negotiate the USB-PD fast charge handshake. The new BMS starts with a conservative current acceptance profile until it has seen at least one full cycle. Charge the phone on standard 5V output for the first complete cycle — do not use a fast charger at this stage. After one full cycle completes, plug in your USB-PD charger and the handshake will resolve at the correct voltage tier.