Fitage Katharina das Grobe 3.7V Replacement Battery 1400mAh

Fitage Katharina das Grobe — 3.7V Li-Polymer Replacement Battery (VKB 66591 312 098)

This is a 3.7V, 1400mAh Li-Polymer replacement battery for the Fitage Katharina das Grobe smartphone. It replaces part number VKB 66591 312 098 directly. Capacity is 1400mAh (5.18Wh), matching the original cell specification.

• Katharina das Grobe fit: This cell matches the voltage rail, physical footprint (41.23 × 33.48 × 8.90mm), and connector orientation of the Katharina das Grobe. The BMS handshake expects a 3.7V nominal Li-Polymer cell — any deviation trips the charge IC and blocks recognition.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a Katharina das Grobe unit. The BMS accepted the cell without error codes, charge termination triggered correctly at 4.2V, and the fuel gauge IC updated state-of-charge readings within the first full cycle.
• First-cycle fuel gauge reset: On first use after installation, disable fast charging and run 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 fast charging pushes current into an uncalibrated cell.

Sudden shutdown at 20–30% on the Katharina das Grobe after a cell swap

A new Li-Polymer cell has a slightly different discharge curve than the aged cell the fuel gauge IC was originally calibrated against. When the phone hits a load spike — from the modem, screen backlight, or GPS — the cell voltage drops sharply below the BMS cutoff threshold even though the reported percentage still shows 20–30%. The phone shuts down to protect the cell. One full discharge-to-near-shutdown followed by a complete charge cycle resets the coulomb counter and aligns the fuel gauge to the new cell curve. After that cycle, shutdowns at high percentages typically stop.

Device not powering on after the replacement cell sat in storage

Li-Polymer cells self-discharge in storage, and if the Katharina das Grobe battery dropped below approximately 2.5V per cell, the BMS enters a deep-discharge lockout state and blocks normal charging to prevent thermal runaway. The phone will show nothing — no charge indicator, no boot screen. Connect the phone to a low-current charger (5V/0.5A or a standard USB wall adapter, not a fast charger) and leave it for 30–60 minutes without interrupting. The BMS uses a trickle pre-charge path at reduced current to bring the cell back above the 3.0V re-enable threshold before handing off to normal CC/CV charging. Once the charge LED or on-screen indicator activates, normal charging has resumed.