MetroPCS M635 Replacement Battery HBU83S 3.7V 700mAh

MetroPCS M635 / Pinnacle 2 — 3.7V Li-ion Replacement Battery (HBU83S)

This is a 3.7V, 700mAh Li-ion cell that replaces the original HBU83S battery in the MetroPCS M635, M636, Pinnacle 2, and related handsets. If the original cell holds charge poorly, causes unexpected shutdowns, or no longer powers the phone through a normal day, this is the direct cell swap. Voltage and physical dimensions match the OEM spec exactly.

• M635 / M636 / Pinnacle 2 platform fit: These models share the same battery bay dimensions, connector orientation, and charge IC voltage profile. The HBU83S and alternate OEM number HB4A1H both map to this cell. One swap covers all listed variants without any adapter or modification.
• Bench tested on actual hardware: We ran this cell through charge, full discharge, and charge again on M635 hardware. The BMS accepted the charge cycle cleanly, the protection circuit tripped at the expected low-voltage cutoff, and the phone woke normally at each stage without error flags.
• Fuel gauge recalibration on first cycle: On first use after installation, run the phone down fully before charging to 100% without interruption. The M635's fuel gauge IC was calibrated against the original cell's discharge curve — one complete cycle on the new cell resets that reference so percentage readings track accurately.

Sudden shutdown at 20–30% on the M635 after a cell swap

This is a voltage cliff problem, not a capacity problem. At high-draw moments — mobile data handoff, screen at full brightness, a call connecting — the new cell briefly drops below the voltage threshold the phone's power IC expects. The phone interprets that sag as a dead battery and cuts out, even though the fuel gauge still shows charge. The fix is one full discharge-to-charge cycle so the fuel gauge IC maps the new cell's actual voltage-to-capacity curve. After calibration, the power IC gets accurate voltage data and stops tripping early.

Phone won't power on after the replacement battery sat in storage

Li-ion cells self-discharge in storage. If this battery sat below 2.5V per cell before installation, the BMS may have entered lockout mode to prevent damage — and the phone will show no response at all, not even a charging indicator. Connect the phone to a wall charger for 15–20 minutes without pressing the power button. The charge IC needs time to trickle current into the cell and bring it above the BMS re-enable threshold. Once voltage climbs past roughly 2.9V, the BMS unlocks and normal charging resumes.