CAT B26 Replacement Battery 3.7V 1350mAh Li-ion

CAT B26 — 3.7V Li-ion Replacement Battery (B26)

This is a 3.7V, 1350mAh Li-ion cell for the CAT B26 rugged smartphone. It fits the B26 directly, matching the original connector and BMS communication protocol. Capacity figure is 1350mAh (5Wh) as specified in the product data.

• CAT B26 platform fit: The B26 uses a single-cell 3.7V Li-ion pack with a proprietary connector and a BMS that handshakes with the device's fuel gauge IC. This replacement matches that voltage rail and connector pinout so the phone's charge controller sees a recognised cell.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge passes on a CAT B26 unit. The BMS reported correct state-of-charge throughout, and charge termination triggered cleanly at 4.2V with no false cutoffs during the modem-active draw phase.
• Fuel gauge recalibration on first use: On first installation, disable fast charging if your B26 supports it, then run one complete discharge-to-charge cycle at standard rate. This gives the fuel gauge IC one full pass to map the new cell's discharge curve before reporting percentage to the OS.

Sudden shutdown at 20–30% on the CAT B26 after a cell swap

The B26's fuel gauge IC holds a discharge model calibrated to the original cell. When a new cell goes in, that model is stale — the IC misjudges the new cell's voltage-to-capacity curve. Under load from the modem or display backlight, the cell's actual terminal voltage drops below the shutdown threshold before the reported percentage catches up. The phone cuts out even though the gauge still shows charge remaining. One full discharge-charge cycle at standard rate resets the coulomb counter and resolves this.

CAT B26 not powering on after the replacement battery sat in storage

Li-ion cells ship at a partial state of charge and self-discharge during storage. If the cell dropped below approximately 2.5V, the BMS enters lockout mode to protect the cell from damage. The phone will show nothing — no boot screen, no charge indicator — which looks like a dead unit but is a BMS protection state. Connect to a wall charger and leave it for 15–20 minutes; the charge IC applies a trickle current to bring the cell above the BMS re-enable threshold, after which normal charging resumes.