About this replacement
Wacom Intuos4 Wireless — 3.7V Li-ion Replacement Battery (ACK-40203)
This 3.7V, 1600mAh Li-ion battery replaces the original cell in the Wacom Intuos4 wireless graphics tablet. It fits the PTK-540WL and PTK-540WL-EN models. Swap it in when the original cell no longer holds charge and the tablet stops running wirelessly through a full work session.
- PTK-540WL and PTK-540WL-EN compatibility: Both variants share the same battery bay geometry, connector pinout, and BMS handshake protocol — one cell covers the full PTK-540WL platform without modification.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a PTK-540WL unit. The onboard BMS accepted the cell without fault codes, and charge termination triggered correctly at full capacity.
- Fuel gauge reset after installation: After fitting this cell, run the tablet down to automatic shutoff on wireless, then charge it uninterrupted to 100%. This gives the fuel gauge IC a known low and known high point calibrated against the new cell — skipping this step is why most users see a wrong percentage immediately after a swap.
Why the PTK-540WL shows an incorrect battery percentage after a cell replacement
The Intuos4 wireless uses a fuel gauge IC that learns cell behaviour over charge cycles. When the original cell ages, the IC recalibrates its capacity map downward to match the degraded cell. A new 1600mAh cell arrives with a full capacity the IC has not yet measured, so the percentage readout is off — sometimes wildly. One complete discharge-to-shutoff followed by a full uninterrupted charge resets the IC's capacity register against the actual cell. After that cycle, the percentage display tracks accurately.
Tablet dropping to 0% and shutting off while the indicator still showed charge
This happens when the fuel gauge IC's stored capacity map no longer matches the cell — common after a swap or after long storage. The IC predicts remaining charge from a stale baseline and miscalculates the voltage cliff. When combined wireless transmission and stylus polling pull current simultaneously, terminal voltage dips sharply and the BMS trips before the displayed percentage reaches zero. Run one full calibration cycle: discharge to auto-shutoff, then charge uninterrupted to 100% without interruption. After that cycle, the IC anchors its map to the correct 3.7V nominal and the shutdowns stop.