T-Mobile MDA Vario III Replacement Battery KAS160 3.7V 1100mAh

T-Mobile MDA Vario III — 3.7V Li-Polymer Replacement Battery (KAS160)

This 3.7V, 1100mAh lithium-polymer cell replaces the original internal battery in the T-Mobile MDA Vario III smartphone. It matches the OEM dimensions at 62.30 × 41.90 × 5.70mm and fits the battery bay without modification. Capacity is 4.07Wh, matching the original specification.

• MDA Vario III platform fit: The Vario III shares its battery footprint and connector pinout across part numbers KAS160, KAIS160, 35H00088-00M, and 35H00086-00M — all refer to the same cell geometry and voltage rail. Any of these OEM references confirms compatibility with this replacement.
• Bench tested on actual hardware: We ran charge and discharge cycles through the MDA Vario III's onboard charge IC. The BMS on this cell accepted the device's charge protocol without interruption, and the protection circuit tripped correctly at the low-voltage cutoff threshold during deep discharge testing.
• Fuel gauge recalibration on first use: After fitting this cell, run one complete discharge to automatic shutdown followed by an uninterrupted charge to 100% before normal use. The MDA Vario III's fuel gauge IC needs a full reference cycle against the new cell's discharge curve — skipping this produces erratic percentage readings for several days.

Why the MDA Vario III shuts down at 20–30% after a cell swap

The MDA Vario III's fuel gauge IC stores a discharge curve calibrated to the original aged cell. A new cell with higher internal consistency hits a steep voltage cliff at a different state-of-charge point than the IC expects. When the screen backlight or radio transmitter draws peak current, terminal voltage drops sharply and the protection circuit interprets it as a depleted cell. The fix is one full reference cycle — discharge to shutdown, charge to 100% uninterrupted — so the coulomb counter resets its endpoint calibration against the new cell.

Battery percentage jumping or freezing after replacement

Erratic percentage display on the Vario III is a fuel gauge IC artefact, not a faulty cell. The IC's learned capacity model still references the old cell's internal resistance profile, so voltage readings during load spikes map to the wrong percentage points on the new curve. This produces jumps of 10–15% or a reading that freezes then snaps forward. Run two full discharge-charge cycles and the IC's adaptive algorithm converges on the new cell — the display stabilises once terminal voltage during load consistently tracks above 3.6V mid-cycle.