About this replacement
Samsung Galaxy C8 Duos — 3.85V Li-Polymer Replacement Battery (EB-BJ731ABE)
This is a 3.85V, 3000mAh Li-Polymer replacement battery for the Samsung Galaxy C8 Duos and C8 Duos TD-LTE, covering SM-C7100, SM-C7108, and related variants. It replaces the original EB-BJ731ABE cell when the factory battery has degraded or lost capacity. Voltage and chemistry match the original specification exactly.
- C8 Duos and TD-LTE variant compatibility: The SM-C7100 and SM-C7108 share the same battery bay geometry, connector pinout, and BMS communication protocol — all variants accept the EB-BJ731ABE cell without modification or adapter.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a Galaxy C8 Duos unit. The BMS handshake completed on the first cycle, charge IC accepted the cell without flagging an error, and the fuel gauge IC began tracking state-of-charge immediately.
- First-cycle fast charge protocol: On first use after installation, disable Samsung Adaptive Fast Charging for one complete discharge-charge cycle. This lets the fuel gauge IC recalibrate its coulomb counter against the new cell's discharge curve before high-current charging pushes load into an uncalibrated state.
Sudden shutdown at 20–30% on the replacement cell
This is the most reported behaviour after a cell swap on the C8 Duos. The fuel gauge IC still holds the discharge curve from the old, degraded cell — so when the new cell hits a voltage point the IC associates with 20–30%, the phone shuts down even though actual charge remains. The fix is a full calibration cycle: discharge the phone until it powers off on its own, then charge uninterrupted to 100% without using the device. After one complete cycle, the coulomb counter resets against the new cell curve and percentage readings stabilise.
USB-PD fast charge not activating on the first cycle after replacement
On the initial charge after fitting a new cell, the charge IC sometimes defaults to standard 5V/1A rather than negotiating the Adaptive Fast Charging protocol. This happens because the BMS on a fresh cell starts in a conservative state until one full cycle is logged. Connect to the original Samsung charger, leave the screen off, and let the first charge complete without interruption. Fast charge negotiation typically activates normally from the second cycle onward.