About this replacement
Asus PadFone / A66 / T20 — 3.7V Li-ion Replacement Battery (SBP-28)
This is a 3.7V, 1500mAh Li-ion cell for the Asus PadFone, A66, and T20. It replaces OEM part SBP-28 (also listed as 0B110-00150000) and fits the smartphone unit — not the tablet dock station. Install it when the original cell no longer holds enough charge for a full day of use.
- PadFone, A66, and T20 compatibility: All three models share the same connector pinout, cell dimensions (51.48 × 50.95 × 5.10mm), and 3.7V nominal voltage rail. The BMS handshake protocol is consistent across this platform, so one cell covers all three variants without modification.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on a PadFone unit. The BMS accepted the cell without fault flags, held voltage above 3.5V under combined screen and modem load, and tapered current correctly at end-of-charge.
- Fuel gauge recalibration after swap: On first use, disable fast charging and run one complete discharge down to automatic shutdown, then charge to 100% uninterrupted. This gives the fuel gauge IC a clean reference cycle against the new cell's discharge curve before high-current charging begins.
Why the PadFone reports wrong battery percentage after a cell swap
The PadFone's fuel gauge IC uses a coulomb counter calibrated against the original cell's impedance and discharge profile. When you fit a new cell, that stored profile no longer matches the actual voltage curve, so the reported percentage drifts from real state-of-charge. The IC needs at least one full discharge-to-shutdown and uninterrupted charge cycle to relearn the curve. Until that cycle completes, percentage jumps of 5–10% in either direction are normal and not a sign of a faulty cell.
Sudden shutdown at 20–30% on the replacement cell
This happens when the cell voltage drops below the modem's minimum supply threshold under load — typically around 3.4V — while the fuel gauge still reads 20–30% remaining. The OS shuts down to protect the BMS rather than because the displayed percentage is accurate. A fresh cell with an uncalibrated fuel gauge IC is especially prone to this on the first few cycles. Run one full discharge cycle without fast charging, and the gauge recalibrates its low-voltage cutoff estimate. If shutdowns continue after three full cycles, check that resting voltage sits at or above 3.7V after a full charge.