I-Mate PDA2K PH26B Replacement Battery 3.7V 4200mAh

I-Mate PDA2K / PDA2K EVDO — 3.7V Li-ion Replacement Battery (PH26B)

This is a 3.7V, 4200mAh Li-ion cell that replaces the original battery in the I-Mate PDA2K and PDA2K EVDO. Both are Windows Mobile PDAs from the mid-2000s, and their original batteries are long past useful service life. Capacity is 4200mAh — identical to the OEM spec listed under part numbers PH26B and AHTXDSSN.

• PDA2K and PDA2K EVDO fitment: Both variants share the same battery bay dimensions, connector pinout, and BMS handshake. The EVDO model adds CDMA radio hardware but draws from the same 3.7V rail, so the same cell fits without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge while monitoring BMS communication with the host device. The protection circuit responded correctly to charge termination and low-voltage cutoff at expected thresholds.
• Fuel gauge recalibration on first install: After fitting this cell, run one complete discharge down to automatic shutdown, then charge uninterrupted to 100% before normal use. The PDA2K's fuel gauge IC was calibrated to the old cell's discharge curve — skipping this step causes the reported percentage to drift by 15–25% from the actual state of charge.

Why the PDA2K reports wrong battery percentage after a cell swap

The PDA2K uses a coulomb-counting fuel gauge IC that builds its charge model against a specific cell's discharge curve over time. When you replace the cell, the IC still references the old degraded curve — not the new one. This makes the percentage display unreliable from the first boot. One full discharge-to-shutdown followed by a complete uninterrupted charge forces the IC to reset its reference points against the new cell. After that single cycle, reported percentage tracks actual charge state accurately.

Sudden shutdown at 20–30% on the replacement cell

This happens when the device draws a high current spike — typically during a radio handoff or screen wake — and the cell voltage drops sharply under load. If the fuel gauge IC hasn't recalibrated yet, it reads 25% while the actual resting voltage is already near the BMS cutoff floor. The BMS trips, and the device shuts down without warning. Run the recalibration cycle first. If shutdowns persist after one full cycle, check resting voltage with the device off — it should read between 3.7V and 4.2V; anything below 3.6V at rest indicates a cell that did not recover from deep discharge in storage.