CAT S50 Li-Polymer Compatible Battery 3.8V 2600mAh

CAT S50 — 3.8V Li-Polymer Replacement Battery (CUBA-BL-00-S50-000)

This 3.8V, 2600mAh Li-Polymer cell is a direct replacement for the CAT S50 rugged smartphone. It fits the S50 exactly, matching the original dimensions of 57.70 × 56.00 × 6.30mm. Swap it when the original cell no longer holds charge through a full shift.

• CAT S50 compatibility: The S50 uses a sealed battery bay with a dedicated BMS that handshakes over the board connector. This cell carries the correct OEM part references (S50, CUBA-BL-00-S50-000) so the device firmware recognises it without triggering an authentication error or capacity warning.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the S50 platform. The BMS accepted the cell on the first cycle, charge current stepped correctly through CC/CV stages, and no thermal cutoff events occurred under sustained screen-on load.
• Fuel gauge recalibration on first cycle: After installation, disable fast charging and complete one full discharge down to automatic shutdown, then charge uninterrupted to 100%. This gives the S50's fuel gauge IC one clean pass against the new cell's discharge curve before high-current charging begins on an uncalibrated cell.

Sudden shutdown at 20–30% on the CAT S50 after a cell swap

The S50's fuel gauge IC stores a charge model built from the old cell's discharge curve. A new cell has a different internal resistance profile, so the IC misjudges how much charge remains. When the modem transmits or the screen peaks in brightness, current draw spikes and the cell voltage drops below the BMS cutoff threshold — even though the displayed percentage still reads mid-range. The fix is one full uninterrupted discharge-to-shutdown followed by a full charge. After that cycle, the coulomb counter has enough data to remap the capacity curve to the new cell.

CAT S50 not powering on after the replacement battery sat in storage

Li-Polymer cells self-discharge in storage. If this cell sat long enough to drop below 2.5V per cell, the BMS enters a lockout state and the phone will not respond to the power button. Connect the S50 to a wall charger — not a USB hub or laptop port — and leave it for 20–30 minutes without pressing anything. The charge IC delivers a low trickle current to bring the cell above the BMS recovery threshold, typically around 2.7V, before switching to normal CC charge. Once the charging indicator appears on screen, the BMS has cleared the lockout.