Sanyo IS01 Replacement Battery SA001UAA 3.7V 650mAh

Sanyo IS01 / SA001 Series — 3.7V Li-ion Replacement Battery (SA001UAA)

This 3.7V 650mAh Li-ion cell replaces the original SA001UAA battery in the Sanyo IS01, SA001, and SA002. All three share the same battery bay dimensions and connector, so one part number covers the full range. Capacity is rated at 2.41Wh — matching the original specification.

• IS01, SA001, SA002 compatibility: These three devices share an identical battery bay at 53.70 × 34.80 × 3.80mm, the same 3.7V nominal rail, and the same connector pinout. The BMS handshake across all three reads the same authentication pulse, so one cell fits without modification.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on the IS01 platform. The BMS accepted the cell without triggering a fault, charge termination fired correctly at 4.2V, and low-voltage cutoff engaged at the expected floor without locking the board.
• Fuel gauge recalibration on first use: On the IS01, disable any fast-charge or sync-heavy background tasks during the first complete discharge-charge cycle. The fuel gauge IC needs one uninterrupted cycle against the new cell's discharge curve before it reports percentage accurately — heavy CPU or radio load during that first cycle skews the calibration baseline.

Why the IS01 reports wrong battery percentage after a cell swap

The IS01 uses a fuel gauge IC that builds its capacity model from accumulated charge and discharge data tied to the original cell's internal resistance curve. When you install a new cell, the IC still references the old curve. This makes the reported percentage drift — often reading 100% earlier than actual full charge or dropping suddenly at low levels. One full uninterrupted discharge-charge cycle lets the coulomb counter reset its baseline against the new cell. After that cycle, percentage reporting stabilises.

Sudden shutdown at 20–30% on the replacement cell

A 650mAh cell at this capacity tier has a steep voltage cliff below 3.6V. When the IS01's display and radio stack draw current simultaneously, voltage sags faster than the fuel gauge IC tracks — the board sees a voltage below its cutoff threshold before the reported percentage reaches zero. This is a cell chemistry characteristic, not a fault. If shutdowns happen consistently at the same percentage, run one full calibration cycle first. If the problem persists after calibration, check that the battery contact pins in the bay are clean and making full contact — a partial connection increases effective load resistance and accelerates the sag.