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 pack rated at 3300mAh (51.48Wh). It fits the Festool TDK15.6 cordless drill, PS 400, and T15+3 models. Use it for fastening, boring, and light drilling tasks where the original BPS15.6 pack has degraded or failed.
- TDK15.6, PS 400, and T15+3 compatibility: These three models share the same 15.6V battery rail, connector footprint, and BMS handshake protocol. One pack fits all three without modification.
- Bench tested on actual hardware: We ran this pack through full charge and discharge cycles on a TDK15.6 drill. The BMS held stable through repeated trigger pulls and showed no overcurrent trips during normal fastening loads.
- Ni-MH break-in on the TDK15.6: Run the drill at half load for two full charge-discharge cycles before tackling heavy fastening work. This allows the BMS to profile the motor's inrush current draw and set accurate overcurrent thresholds before you push maximum torque.
BMS overcurrent trip on motor-start inrush in the TDK15.6
On the first few trigger pulls, the TDK15.6 motor draws a sharp inrush current spike — often three to five times the steady running current. A new Ni-MH pack with a freshly calibrated BMS may read this spike as a fault and cut power immediately. This is not a defective battery. Run two partial load cycles first so the BMS logs the motor's actual inrush signature and stops flagging it as an overcurrent event.
Charger not recognising the BPS15.6 pack after storage
Ni-MH cells self-discharge during storage, and if the pack sits long enough, cell voltage drops below the charger's acceptance threshold. The charger sees a voltage too low to confirm a healthy pack and refuses to begin a charge cycle. To recover it, place the pack in the charger and hold it there — some Festool chargers will run a trickle pre-charge to bring cells above the acceptance floor before switching to full current. If the charger still rejects the pack after 30 minutes, check that the terminal voltage reads at least 10V across the pack with a multimeter before trying again.