T-Mobile Tap HB5A2H Replacement Battery 3.7V 700mAh

T-Mobile Tap / Pulse Mini — 3.7V Li-ion Replacement Battery (HB5A2H)

This is a 3.7V, 700mAh Li-ion replacement cell for the T-Mobile Tap and Pulse Mini smartphones. It replaces OEM part numbers HB5A2H and BTR7519. The battery restores power to a phone that won't hold a charge or won't turn on due to a degraded original cell.

• Tap and Pulse Mini fitment: Both models share the same battery bay dimensions and connector pinout, so this single cell covers both. The BMS handshake voltage and charge termination threshold match the original charge IC on each board.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the Tap platform. The BMS accepted charge termination at 4.2V and tripped low-voltage cutoff correctly before the cell dropped below safe discharge limits.
• Fuel gauge recalibration on first use: After fitting this cell, run one full discharge to automatic shutoff, then charge uninterrupted to 100% before normal use. The phone's coulomb counter is still calibrated to the old cell's discharge curve — skipping this step causes the percentage reading to jump or report incorrect values.

Why the Tap reports wrong battery percentage after a cell swap

The Tap uses a fuel gauge IC that builds its capacity model from accumulated charge and discharge data on the original cell. When you install a new cell, that learned curve no longer matches the new cell's actual voltage-to-capacity relationship. The IC keeps using the old model, so it reports percentages that don't reflect real remaining charge. One complete discharge-charge cycle forces the fuel gauge to rebuild its reference against the new cell's actual discharge profile.

Sudden shutdown at 20–30% remaining on the replacement cell

This happens when the modem radio or display spikes current draw faster than the cell can sustain voltage at that state of charge. At 20–30% remaining, cell impedance rises — a sudden load pulls terminal voltage below the BMS cutoff threshold before the fuel gauge catches up, and the phone shuts off. It's not a faulty cell; it's the voltage cliff on a small-capacity 700mAh cell under peak modem load. Completing a full recalibration cycle first reduces the frequency of early cutoffs by giving the fuel gauge an accurate low-end voltage reference.