About this replacement
Lenovo ThinkPad 1838 Series — 7.4V Li-Polymer Replacement Battery (42T4963)
This 7.4V, 3200mAh (23.68Wh) lithium-polymer battery replaces the original power cell in the Lenovo ThinkPad 1838 tablet. It fits the ThinkPad 1838, 1838 10.1, 1838-25U, and 1838-22U. OEM part numbers covered include 42T4963, 42T4964, 42T4985, 42T4965, and 42T4966.
- ThinkPad 1838 variant coverage: The 1838, 1838 10.1, 1838-25U, and 1838-22U share the same physical cell format, connector pinout, and BMS handshake protocol. One battery covers all four variants without modification.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a ThinkPad 1838 unit. The BMS accepted the cell without fault codes, completed a full charge cycle, and the tablet powered on and off cleanly across multiple sessions.
- Fuel gauge recalibration after swap: After fitting this battery, run the tablet down to automatic shutoff — do not force-power it off. Then charge it uninterrupted to 100%. This gives the fuel gauge IC a clean reference point against the new cell and corrects percentage drift that appears immediately after installation.
ThinkPad 1838 shutting down at 15–25% remaining
This happens when the tablet runs the display at full brightness alongside active Wi-Fi — combined draw pulls the cell voltage down faster than the fuel gauge expects. The BMS reads a voltage threshold that triggers a protection cutoff, but the OS still shows charge remaining. The fix is one full recalibration cycle: discharge to automatic shutoff, then charge to 100% without interruption. After that cycle, the fuel gauge aligns with the actual cell voltage curve and premature shutoffs stop.
Fast charging not available after battery replacement
The ThinkPad 1838 charge controller needs at least one completed charge cycle before it confirms USB-PD negotiation parameters with a new cell. Until that cycle completes, the tablet defaults to standard charge rates as a safety measure. Plug in the tablet and let it charge from low to 100% without unplugging partway. After that first full cycle, fast charge becomes available again on compatible adapters.