CAT S42 Replacement Battery 3.85V 4100mAh 596266

CAT S42 / S32 — 3.85V Li-Polymer Replacement Battery (596266 / TPJ20A05P)

This is a 3.85V, 4100mAh Li-Polymer replacement battery for the CAT S42 and S32 smartphones. It matches OEM part numbers 596266 and TPJ20A05P. Install it when the original cell no longer holds enough charge for a full day of calls, messaging, and app use.

• S42 and S32 compatibility: Both models share the same battery bay dimensions, voltage rail, and BMS connector pinout. The 596266 cell fits either device without modification — same 68.50 × 61.80 × 6.00mm footprint and identical fuel gauge handshake.
• Bench tested on actual hardware: We ran this cell through full charge and discharge cycles on the S42. The BMS accepted charge from both standard 5V and fast-charge inputs. Voltage held steady above 3.6V under combined screen and modem load, with no unexpected cutoff events.
• Fuel gauge recalibration on first use: After fitting this cell, disable fast charging for the first complete discharge-charge cycle. The fuel gauge IC on the S42 is calibrated to the original cell's discharge curve. One slow cycle lets it recalibrate against the new cell before high-current charging is applied to an uncalibrated state.

Sudden shutdown at 20–30% on the CAT S42 after a cell swap

The S42 fuel gauge IC stores a discharge model built from hundreds of cycles on the original cell. When a new cell goes in, that model no longer matches the actual voltage-to-capacity curve of the replacement. Under peak modem or screen load, the phone sees a voltage dip that the old model interprets as empty — even if the cell is at 25% real capacity. The fix is one full discharge-charge cycle with fast charging off. After that single cycle, the coulomb counter resets its endpoints and the shutdowns stop.

Phone warm near the battery on first charge after replacement

A fresh Li-Polymer cell has higher internal impedance than a broken-in one. The charge IC pushes current into that higher impedance, and the energy that doesn't go into the cell goes out as heat. This is normal for the first two or three charge cycles and fades as the cell's impedance drops with use. If warmth continues past the third charge or the phone becomes hot rather than warm, check that the replacement cell is seated flat against the chassis — a lifted edge traps heat against the back cover. Charge at room temperature and the issue resolves itself by cycle three.