About this replacement
HTC One E9 / One E9 Plus — 3.85V Li-Polymer Replacement Battery (35H00239-00M)
This is a 3.85V, 2800mAh lithium-polymer cell for the HTC One E9, One E9 Plus, A55, One E9w, and related variants. It replaces OEM part numbers 35H00239-00M, BOPJX100, B0PJX100, and 35H00239-09M. Fit this battery when the original cell no longer holds a charge or shuts down unexpectedly under load.
- E9 series compatibility: The One E9, E9 Plus, E9w, and A55 all share the same battery bay geometry, 3.85V nominal voltage rail, and flex connector pinout — which is why a single cell covers the full cluster. The BMS handshake is identical across these variants, so the fuel gauge IC initialises without modification.
- Bench tested on actual hardware: We cycled this cell on an E9 unit through charge, load, and cutoff. The BMS held the 4.35V charge ceiling correctly and tripped the low-voltage cutoff at the expected floor without false shutdowns mid-cycle.
- Fuel gauge recalibration on first cycle: On first use after installation, disable fast charging and run one full discharge-to-charge cycle. This gives the fuel gauge IC a clean reference against the new cell's discharge curve before high-current charging pushes current into an uncalibrated cell.
Sudden shutdown at 20–30% on the replacement cell
A new lithium-polymer cell has a steeper voltage cliff than a worn cell the fuel gauge IC was previously calibrated to. When the modem transmits or the screen peaks, current draw spikes and cell voltage drops sharply — past the BMS cutoff threshold — even though the OS still shows 20–30% remaining. The fuel gauge's coulomb counter is reading against an old discharge curve, so the percentage displayed doesn't match actual cell voltage. One complete discharge cycle from 100% down to automatic shutdown, followed by a full charge, lets the IC remap its curve to the new cell. After that cycle, shutdowns at falsely high percentages stop.
Device won't power on after the battery sat in storage
Lithium-polymer cells self-discharge during storage. If the cell drops below approximately 2.5V, the BMS enters a deep-discharge lockout state and blocks normal charge current to prevent thermal runaway on a potentially damaged cell. Plugging into a standard charger appears to do nothing — the phone shows no charging animation. Connect the phone to a low-current USB source (a PC USB-A port, not a fast charger) and leave it for 20–30 minutes; the trickle current is enough to bring the cell above the BMS re-entry threshold, after which normal charging resumes. Once the phone shows a charging indicator, switch to the wall adapter to complete the charge.