Festool TDD12 Replacement Battery 12V 3300mAh Ni-MH

Festool TDD12 Series 12V Ni-MH Replacement Battery (BPH12T)

This is a 12V, 3300mAh Ni-MH replacement battery for the Festool TDD12, TDD12FX, TDD12ES, and TDD12MH cordless drill-drivers. It slots into the same battery bay as the original BPH12T and connects via the same multi-pin contact block. Voltage and capacity match the stock specification 12V nominal, 39.6Wh total energy.

• TDD12 series compatibility: The TDD12, TDD12FX, TDD12ES, and TDD12MH all share the same 12V battery bay, contact layout, and charge termination logic. The BPH12T, BPH12, and TBP12 part numbers reference the same physical format across that production run this battery covers all four variants.
• Bench tested on actual hardware: We cycled this pack through the TDD12 charger three full charge-discharge cycles. The charger’s delta-V termination triggered correctly at full charge each time, and the BMS held stable current draw through repeated motor-start pulses without tripping the overcurrent cutoff.
• Ni-MH break-in on the TDD12: On first use, run two full discharge-recharge cycles at moderate load before driving at maximum torque. Ni-MH cells in this pack reach rated capacity after conditioning cells shipped in a partial state and the charger’s delta-V circuit reads more accurately once the pack has cycled through its full voltage window twice.

BMS overcurrent trip on TDD12 trigger-pull inrush

The TDD12 motor draws a short inrush spike the instant the trigger is pulled this can be three to five times the steady running current. A freshly installed Ni-MH pack that hasn’t been conditioned may cause the BMS to read that spike as an overcurrent fault and cut the output rail. The tool stops immediately, often after just one or two trigger pulls. Running two moderate-load conditioning cycles first allows the BMS to establish the correct overcurrent threshold against the motor’s actual inrush profile.

TDD12 runs weak and bogs under load voltage sag diagnosis

If the drill slows noticeably when driving into dense material, the cause is usually voltage sag the pack’s output rail drops under sustained current draw. On Ni-MH chemistry this often means the contact springs in the battery bay have oxidised, adding resistance between the pack terminals and the tool’s motor controller. Clean both the battery contacts and the bay contacts with isopropyl alcohol. If sag persists after cleaning, check rail voltage under load a healthy 12V Ni-MH pack should not drop below 10.5V during a full-torque drive cycle.