Telefonica TSM400 Compatible Battery 3.7V 1700mAh

Telefonica TSM400 — 3.7V Li-Polymer Replacement Battery (35H10008-80)

This is a 3.7V, 1700mAh Li-Polymer battery for the Telefonica TSM400 smartphone. It replaces OEM part number 35H10008-80 directly. At 94.33 × 50.53 × 3.49mm, it fits the original battery bay without modification.

• TSM400 cell compatibility: The TSM400 runs a single-cell Li-Polymer architecture at 3.7V nominal. The BMS in this phone communicates with the charge IC over a thermistor line — the replacement cell matches the NTC resistance profile the phone expects, so the charge IC does not throttle or reject the session.
• Bench tested on actual hardware: We ran the TSM400 through full charge and discharge cycles with this cell fitted. The BMS accepted the handshake on first cycle, charge current stepped down correctly at 4.2V, and cutoff triggered cleanly at the low-voltage threshold without a hard lockout.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging and let the phone complete one full discharge-charge cycle at standard current. This gives the fuel gauge IC time to map the new cell's discharge curve before high-current charging is applied to an uncalibrated cell.

Sudden shutdown at 20–30% on the TSM400 after a cell swap

This happens because the fuel gauge IC is still using the discharge curve it learned from the old, degraded cell. The new cell has a steeper voltage cliff at the low end — the phone reads 25% but the actual cell voltage has already dropped below what the modem and display can sustain under load. The result is an immediate shutdown with no warning. One full discharge down to auto-off, followed by a full charge, forces the coulomb counter to recalibrate against the new cell's actual curve. After that cycle, the percentage readout tracks correctly.

TSM400 not powering on after the replacement battery sat in storage

Li-Polymer cells self-discharge in storage. If this battery has been stored for several months, the cell voltage may have dropped below 2.5V — the threshold at which the BMS trips into lockout to prevent damage. The phone will show no response on the power button and no charge indicator when plugged in. Connect the phone to a wall adapter, not a PC port, and leave it for 20–30 minutes without pressing anything. The charge IC on most units will trickle current into the cell until it clears 3.0V, at which point the BMS resets and normal charging resumes.