Swissvoice MP01 TJB-1 Replacement Battery 3.7V 1000mAh

Swissvoice MP01 — 3.7V Li-ion Replacement Battery (TJB-1)

This is a 3.7V Li-ion battery rated at 1000mAh (3.7Wh), built to the TJB-1 specification. It fits the Swissvoice MP01 mobile phone — a compact handset used primarily for voice calls and basic messaging. If the original cell no longer holds a charge or the phone dies unpredictably, this is the direct swap.

• MP01 platform fit: The MP01 uses a single-cell Li-ion pack at 3.7V nominal. The TJB-1 format matches the connector pinout and physical footprint — 54.61 × 35.16 × 5.31mm — so the cell seats correctly without case pressure or connector strain.
• Bench tested on actual hardware: We cycled this cell through charge and load on a matched test rig. The BMS held cutoff correctly at both the low-voltage floor and charge termination point. No false trips under the MP01's typical modem and screen draw.
• Fuel gauge recalibration on first install: After fitting a new cell, run the MP01 from 100% down to auto-shutdown once before recharging. The phone's fuel gauge IC was calibrated to the old cell's discharge curve — one full cycle rewrites that reference and prevents the percentage jumping erratically in normal use.

Why the MP01 reports wrong battery percentage after a cell swap

The MP01's fuel gauge IC tracks capacity using a stored discharge curve from the original cell. When a new cell goes in, that curve no longer matches actual cell behaviour. The gauge reads voltage and estimates percentage against stale reference data, so it can report 40% when the cell is nearly empty — or show a sudden drop from 60% to 10%. One full discharge-to-shutdown followed by a complete charge resets the coulomb counter against the new cell's actual curve.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage collapses under load before the gauge registers a low reading. During a call, the modem draws a short current spike — if the cell cannot sustain voltage above roughly 3.2V under that load, the phone's protection circuit cuts power immediately. The gauge still shows 20–30% because it was reading resting voltage, not loaded voltage. After the first full calibration cycle, the gauge tracks this more accurately and the shutdowns typically stop.