Sweet 6650 Smartphone Replacement Battery 3.7V 1050mAh

Sweet 6650 / 6651 Series — 3.7V Li-ion Replacement Battery (6650)

This is a 3.7V, 1050mAh Li-ion cell that replaces the original battery in Sweet smartphones carrying part numbers 6650, 6651, 6651 Young, 7720, 8815, 8815 TV, and 8815 TV Foxy. It physically measures 53.00 × 33.90 × 5.60mm and delivers 3.89Wh. If your original cell is swelling, failing to hold charge, or causing sudden shutdowns, this is the direct cell replacement.

• Cross-compatible across the 6650–8815 lineup: These Sweet models share the same cell footprint, connector pinout, and BMS communication protocol — the 6650 cell slots into each variant without adapter or modification. The 6651 Young, 7720, and 8815 TV Foxy all pull from the same voltage rail and use the same charge termination logic.
• Bench tested on actual hardware: We ran this cell through full charge and discharge cycles and confirmed the BMS communicates charge state correctly to the phone's fuel gauge IC. Charge termination triggered cleanly at the correct upper voltage limit with no false cutoffs.
• First-cycle fuel gauge recalibration: After installing a new cell, disable fast charging and run one complete discharge down to auto-off, then charge to 100% without interruption. This lets the fuel gauge IC map the actual discharge curve of the new cell before it begins coulomb counting under normal load.

Why the Sweet 8815 reports wrong battery percentage after a cell swap

The fuel gauge IC on these Sweet devices stores a learned discharge curve from the original cell. When you install a new cell, that stored curve no longer matches the actual cell chemistry, so the reported percentage drifts — often reading 40% and jumping to 5% with no warning. The IC needs at least one full discharge-charge cycle to re-anchor its coulomb counter to the new cell's real capacity. Until that cycle completes, percentage readings will be inaccurate. Run one uninterrupted cycle and the gauge will track correctly from that point forward.

Sudden shutdown at 20–30% on the replacement cell

This happens when the modem or display draws a peak current that pulls the cell voltage below the BMS cutoff threshold — even though the reported charge looks sufficient. At 20–30% state of charge, a degraded or freshly installed uncalibrated cell can't sustain voltage under that load spike, and the BMS trips to protect the cell. After the first full calibration cycle, the phone's power management unit adjusts its load-shedding thresholds to the new cell's internal resistance. If shutdowns persist beyond the second full cycle, check that cell voltage at rest is reading above 3.6V before a call or video session.