Astell&Kern AK300 Replacement Battery CP-AK380 3.8V 3300mAh

Astell&Kern AK300 / AK380 — 3.8V Li-Polymer Replacement Battery (CP-AK380)

This is a 3.8V, 3300mAh lithium-polymer battery for the Astell&Kern AK300 and AK380 portable high-resolution audio players. It replaces OEM part CP-AK380 and fits the same cell cavity dimensions: 78.00 × 42.64 × 6.26mm. Capacity is 12.54Wh — matched to the original specification.

• AK300 and AK380 compatibility: Both models share the CP-AK380 cell format, the same 3.8V nominal voltage rail, and an identical BMS handshake protocol. One cell fits both units without any hardware modification.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the AK300. The BMS accepted the cell without a fault flag, voltage held steady across the mid-charge range, and the protection circuit tripped correctly at the low-voltage cutoff threshold.
• Post-install charge cycle on the AK300/AK380: After fitting this cell, connect the player to its original charger and let it charge fully before powering on. Media players with depleted cells often enter a deep-discharge protection state that requires slow trickle current before the BMS will accept a standard charge rate. Skipping this step can cause the device to show no charge activity for the first 20–30 minutes.

Battery percentage jumping after a cell swap on the AK300

The AK300 estimates state-of-charge using voltage thresholds calibrated to the original cell's discharge curve. A new cell has a slightly different resting voltage profile, so the indicator can read 80% one moment and drop to 60% minutes later. This is a recalibration issue, not a cell defect. Run two or three full charge-to-discharge cycles and the on-screen percentage will stabilise as the firmware maps the new cell's actual curve.

Playback cutting out before the battery indicator reaches empty

The AK300's audio amplifier draws a brief current spike when driving low-impedance headphones or balanced outputs at high volume. Near the end of a discharge cycle, cell voltage sags under that spike and drops below the BMS cutoff threshold — the player shuts down even though the indicator hasn't reached zero. This isn't a faulty battery; it's the protection circuit doing its job. To reduce premature cutoffs, lower output gain by one step in the AK300's settings and recharge when the indicator reaches 15%.