E-Plus PDA III Replacement Battery 3.7V 4200mAh Li-ion PH26B

E-Plus PDA III — 3.7V Li-ion Replacement Battery (PH26B)

This is a 3.7V, 4200mAh Li-ion replacement battery for the E-Plus PDA III mobile device. It carries OEM part references PH26B and AHTXDSSN. Fit this cell when the original no longer holds charge or the device shuts down unexpectedly under load.

• PDA III compatibility: The PDA III uses a fixed 3.7V single-cell Li-ion architecture. This replacement matches that voltage rail, connector pinout, and BMS handshake protocol — the device powers on and communicates with the battery management system without modification.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a PDA III unit. The BMS accepted the cell on first connection, charge termination triggered correctly at 4.2V, and protection cutoff engaged as expected under over-discharge conditions.
• Fuel gauge recalibration on first use: After fitting this cell, disable fast charging and run one full discharge-to-charge cycle before resuming normal use. The fuel gauge IC on the PDA III calibrates its coulomb counter against the new cell's discharge curve on that first cycle — skipping it leads to inaccurate percentage readings early on.

Sudden shutdown at 20–30% on the PDA III after a cell swap

A new cell has a slightly different internal resistance profile than the aged original. Under heavy load — modem transmit, screen at full brightness, GPS active — the cell voltage drops faster than the fuel gauge expects. The PDA III's protection circuit reads this as a critical low-voltage event and cuts power even though the reported percentage still looks reasonable. One full discharge-charge cycle lets the fuel gauge IC map the actual voltage cliff of the new cell, after which the shutdown threshold tracks correctly. If shutdowns persist beyond two cycles, check that the percentage at shutdown is climbing rather than holding at the same figure.

PDA III not powering on after the replacement battery sat in storage

Li-ion cells self-discharge in storage. If this battery shipped or was stored for several weeks, cell voltage may have dropped below 3.0V — at that point the BMS enters lockout to prevent damage. The PDA III will show no response to the power button and may not register on a standard charger. Connect the device to a wall charger rather than a PC USB port, which delivers more consistent current to wake a locked-out BMS. Leave it on charge for 20–30 minutes before attempting to power on; once voltage climbs above 3.2V the BMS re-initialises and normal charging resumes.