BlackBerry KEYone BAT63108-003 Replacement Battery 3.85V 3400mAh

BlackBerry KEYone — 3.85V Li-Polymer Replacement Battery (BAT63108-003)

This is a 3400mAh (13.09Wh) 3.85V lithium-polymer replacement battery for the BlackBerry KEYone and Mercury smartphones. It replaces the original BAT63108-003 cell and fits BBB100-1 and related KEYone variants. Dimensions are 80.80 × 50.76 × 5.00mm — confirm these against your existing cell before installation.

• KEYone and Mercury compatibility: Both devices share the same battery bay dimensions, connector pinout, and BMS handshake protocol. The KEYone (BBB100-1 and TD-LTE variants) uses the same charge IC communication lines as the Mercury, so one cell part number covers the full range.
• Bench tested on actual hardware: We ran this cell on a KEYone BBB100-1 unit. The BMS accepted the charge handshake immediately, and the fuel gauge IC began tracking state-of-charge within the first partial cycle. No charge rejection or error flags appeared during testing.
• First-cycle fast charging on a new cell: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC recalibrate against the new cell's discharge curve before the charge IC pushes high current into an uncalibrated cell — reducing the risk of inaccurate percentage readings early on.

Sudden shutdown at 20–30% on the KEYone after a cell swap

A new cell has a different internal resistance curve than the degraded cell the fuel gauge IC was calibrated to. When the modem fires up during a call or data burst, current draw spikes and voltage drops faster than the gauge predicts. The phone interprets this as a hard undervoltage event and shuts down, even though the displayed percentage still shows capacity remaining. One full discharge-to-shutdown followed by a complete charge cycle resets the coulomb counter and aligns the gauge to the new cell's actual voltage cliff — typically around 3.4–3.5V under load.

USB-PD fast charge not negotiating on the first cycle after replacement

After a cell swap, the KEYone's charge IC sometimes defaults to standard 5V charging on the first connection while the BMS completes its initialisation sequence. This is not a fault with the charger or the new cell. Disconnect the cable, wait 10 seconds, and reconnect — the PD negotiation handshake retries and the fast charge protocol typically resumes. If it persists past the first full cycle, check that the USB-C port is clean and the cable supports USB-PD at the rated amperage.