About this replacement
Astell&Kern AK70 — 3.8V Li-Polymer Replacement Battery (SR605056)
This is a 3.8V, 2600mAh lithium-polymer battery for the Astell&Kern AK70 portable high-resolution audio player. It replaces OEM part SR605056 directly. Dimensions are 56.15 × 49.60 × 6.00mm — verify these against your existing cell before ordering.
- AK70 platform fit: The AK70 uses a flat Li-Polymer pouch cell with a three-pin connector tied to the player's fuel gauge IC. Voltage must land at 3.8V nominal — cells outside this rail cause the AK70 to misread charge state from the first boot.
- Bench tested on actual hardware: We cycled this cell through the AK70's charge controller and confirmed the BMS accepted full charge termination at 4.35V without tripping the protection circuit. Discharge cutoff at the low end held steady without premature shutdown.
- Post-install charge protocol for the AK70: After fitting a new cell, connect the AK70 to its original charger for a full uninterrupted charge before powering on. The AK70's fuel gauge IC needs one complete charge cycle to anchor its capacity baseline — skipping this causes the percentage readout to jump erratically for the first several sessions.
Why the AK70 battery percentage jumps after a cell swap
The AK70 uses a coulomb-counting fuel gauge that anchors its full-charge reference point during the first complete charge cycle on a new cell. When you install a fresh battery, that reference is blank. The gauge extrapolates from stored voltage thresholds, which don't match the new cell's curve exactly. Run two or three full charge-discharge cycles and the percentage display stabilises — no firmware update or factory reset required.
Playback cutting out before the AK70 shows empty
The AK70's audio amplifier draws harder at high volume than the rest of the circuit. Near the end of a discharge cycle, cell voltage sags under that load and briefly dips below the BMS protection threshold — the player shuts down even though the fuel gauge still shows a few percent remaining. This is a voltage sag issue, not a capacity issue. Lower the output volume slightly when the battery is below 15% and cutouts stop.