Toshiba E400 Compatible Battery LAB503759C 3.7V 1000mAh

Toshiba E400 / E410 — 3.7V Li-Polymer Replacement Battery (LAB503759C)

This is a 3.7V, 1000mAh lithium-polymer cell that replaces the LAB503759C battery in the Toshiba E400 and E410 pocket PCs. These early-2000s PDAs rely on a single flat Li-Po cell to power the processor, RAM, and display. When the original cell degrades, the device loses charge quickly or won't hold enough voltage to boot.

• E400 and E410 platform fit: Both models use the same battery bay dimensions and the same 3.7V single-cell Li-Po arrangement. The connector pinout and BMS communication protocol are identical across the two, so one cell covers both units without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on an E400 unit. The BMS accepted the cell without fault flags, regulated charge termination cleanly at 4.2V, and held the low-voltage cutoff at the expected threshold without premature shutdown.
• RAM state before you remove the old battery: Sync all open data to the host PC before pulling the original cell. The E400 stores active application state and unsaved contacts in volatile SRAM — that data disappears the moment battery voltage drops to zero. A full ActiveSync before the swap takes 60 seconds and prevents data loss.

Why the E400 won't boot after a battery swap

A freshly shipped Li-Po cell typically arrives at 30–50% state of charge — enough for storage, not enough for the E400's boot sequence. The device checks for a minimum voltage threshold before committing to a full boot. If that threshold isn't met, the unit either shows a low-battery warning and halts, or shows nothing at all. Connect the E400 to its charger for at least two hours before attempting the first power-on after a battery replacement.

E400 calendar and contacts missing after the new battery goes in

The E400 keeps its operating system in ROM, but open records, calendar entries, and installed third-party apps live in volatile SRAM. SRAM requires continuous power — even a brief gap during a battery swap is enough to wipe it. If data is already gone, connect to ActiveSync immediately and restore from the last backup. Going forward, perform a full sync before every battery removal to avoid repeating the loss.