About this replacement
Festool TDK15.6 / PS 400 / T15+3 — 15.6V Ni-MH Replacement Battery (BPS15.6)
This is a 15.6V Ni-MH replacement battery with 2100mAh capacity for the Festool TDK15.6, PS 400, and T15+3 cordless drills. It replaces OEM part numbers BPS15.6, BPS15,6S, 492 269, and 491 823. Physical dimensions match the original pack at 124.45 × 74.73 × 62.39mm, so it seats and locks without modification.
- TDK15.6 / PS 400 / T15+3 platform fit: These three Festool models share the same 15.6V battery rail, connector pinout, and charge-communication protocol. One pack covers all three tools without adapter or firmware differences to account for.
- Bench tested on actual hardware: We cycled this pack on the TDK15.6 through full charge and discharge sequences. The cell protection circuit held within spec across both trigger-pull inrush and sustained fastening loads, with no false overcurrent trips detected.
- Ni-MH break-in on first use: Run the drill at moderate torque settings through two full discharge-and-charge cycles before maxing out the clutch. Ni-MH cells need conditioning cycles to reach rated capacity — skipping this leaves measurable capacity on the table from day one.
Why the TDK15.6 cuts out on hard trigger pulls
At the moment the motor starts, it draws a brief current spike several times higher than its running load. On a Ni-MH pack that has been sitting in storage, internal resistance rises and that spike can trip the cell protection circuit before the motor reaches operating speed. The result is an immediate cutout the instant you pull the trigger. Condition the pack with two full cycles first — this lowers internal resistance and allows the protection circuit to handle the inrush without false-tripping.
Charger not recognising the pack after storage
Festool's original chargers use a voltage-detect handshake before committing to a charge cycle. If the pack has self-discharged below roughly 10V, the charger reads it as a fault and refuses to start. Place the pack in the charger, remove it after 30 seconds, and reinsert — some chargers will attempt a recovery pulse on the second insertion. If that fails, a brief trickle from a compatible Ni-MH charger set to recovery mode can bring the pack back above the acceptance threshold, typically 10.5V, at which point the Festool charger will proceed normally.