About this replacement
HTC Desire 816 / A5 — 3.8V Li-Polymer Replacement Battery (B0P9C100)
This is a 3.8V, 2600mAh Li-Polymer cell that replaces the original battery in the HTC Desire 816, Desire 816w, Desire 816 Dual SIM, and A5 series smartphones. It matches the OEM part numbers B0P9C100, 35H00220-01M, and 35H00220-00M. Install it when the original cell no longer holds enough charge for a full day of use.
- Desire 816 / A5 platform fit: These models share the same battery bay dimensions, connector pinout, and BMS communication protocol. The 74.95 × 69.50 × 3.28mm cell fits without modification, and the charge IC handshake proceeds normally on first boot.
- Bench tested on actual hardware: We cycled this cell through full charge and discharge on a Desire 816 unit. The BMS accepted charge termination correctly at 4.35V, and no thermal cutoff events triggered during the test cycle.
- Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC build an accurate discharge curve against the new cell before high-current charging begins on an uncalibrated coulomb counter.
Sudden shutdown at 20–30% on the Desire 816 after a cell swap
The Desire 816 uses a coulomb-counter fuel gauge that was calibrated to the old cell's discharge curve. When a new cell goes in, the reported state of charge does not match actual cell voltage. Under modem load or screen brightness spikes, the new cell's voltage dips below the BMS cutoff threshold before the OS percentage reaches zero — and the phone shuts off. One full slow discharge to 0% followed by an uninterrupted charge to 100% resets the counter. After that cycle, shutdowns at 20–30% typically stop.
Phone won't power on after the replacement battery sat in storage
Li-Polymer cells self-discharge during storage, and if this battery dropped below approximately 2.5V per cell, the BMS entered deep-discharge lockout to prevent damage. Plugging in a charger may show no response for the first 10–15 minutes while the charge IC trickle-charges the cell back above the BMS recovery threshold. Leave the phone connected without pressing the power button. Once cell voltage climbs above 3.0V, the BMS re-initialises and the device will boot normally.