T-Mobile MDA i Compatible Battery 3.7V 1700mAh Li-Polymer

T-Mobile MDA i — 3.7V Li-Polymer Replacement Battery (35H10008-80)

This 3.7V, 1700mAh lithium-polymer cell replaces the OEM battery in the T-Mobile MDA i Windows Mobile smartphone. It matches the original part number 35H10008-80 and fits the MDA i's battery bay without modification. Voltage, capacity, and connector orientation match factory spec.

• MDA i platform fit: The MDA i runs a single-cell Li-Polymer architecture at 3.7V nominal. The BMS on this device expects a cell with a discharge curve that stays above 3.0V under modem and display load. This replacement cell matches that curve, so the handset's charge IC accepts it without fault codes.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on an MDA i unit. The BMS accepted the cell on first connection, charge termination triggered correctly at 4.2V, and no thermal events occurred during the full charge cycle.
• Fuel gauge recalibration on first use: After installing this cell, run the MDA i from a full charge down to automatic shutdown once before recharging. The fuel gauge IC on the MDA i was calibrated to the old cell's discharge curve — one complete cycle resets that reference point and gives you accurate percentage readings going forward.

Why the MDA i reports wrong battery percentage after a cell swap

The MDA i uses a coulomb-counting fuel gauge IC that builds its charge model from the previous cell's discharge history. When you install a new cell, that stored model no longer matches the actual discharge curve of the replacement. The gauge continues using stale data, so the percentage display drifts — often reading 20–40% higher or lower than actual state of charge. One full discharge-to-shutdown followed by a complete charge to 4.2V forces the IC to rewrite its reference and re-anchor the percentage scale to the new cell.

Sudden shutdown at 20–30% on the replacement cell

This happens when the fuel gauge IC has not yet recalibrated and the displayed percentage no longer reflects real cell voltage. The MDA i's modem and backlight draw current spikes that pull cell voltage below the BMS cutoff threshold — typically around 3.0V — before the display reads zero. The phone cuts power instantly to protect the cell. To resolve it, allow the fuel gauge one full discharge cycle so the IC can map the new cell's voltage-to-capacity relationship accurately and trigger shutdown at the correct point.