Bosch PT6MXJ Cordless Phone Compatible Battery 3.6V 1500mAh

Bosch CT-XTAM521 — 3.6V Ni-MH Replacement Battery (PT6MXJ)

This is a 3.6V, 1500mAh Ni-MH replacement battery for the Bosch CT-XTAM521 cordless DECT phone handset. It matches the OEM part number PT6MXJ and fits the handset battery compartment directly. Voltage, capacity, and connector are spec-matched to the original Bosch pack.

• CT-XTAM521 handset fit: The CT-XTAM521 uses a 3.6V three-cell Ni-MH pack with a specific footprint — 49.80 × 42.90 × 14.40mm. The base station's charging circuit reads the voltage curve of a Ni-MH pack; swapping to a different chemistry will cause charge errors or no-charge conditions.
• Bench tested on actual hardware: We cycled this pack through the CT-XTAM521 base station and confirmed the BMS accepted the charge handshake on the first seat. Charge termination triggered cleanly at full capacity with no error light.
• First charge on a new Ni-MH handset pack: After installing, place the handset in the base for a full 16-hour charge before first use. Ni-MH cordless phone batteries arrive partially discharged from storage, and a slow first charge lets the cells reach rated capacity. Skipping this step will leave you with noticeably shorter talk time on the first few cycles.

Talk time shorter than the original battery after replacement

New Ni-MH cells ship in a partially discharged state and need three to five full charge-discharge cycles to reach their rated 1500mAh capacity. The CT-XTAM521 base station uses a trickle-charge circuit that tops up slowly — so each of those first cycles may feel short. By cycle four or five, capacity should match the original pack. If talk time is still noticeably short after five full cycles, check that the handset is seating firmly in the base cradle contacts.

Base station shows no charge or error light after fitting the new pack

A Ni-MH pack that has sat in a warehouse can drop to a voltage below the base station's charge-acceptance threshold — typically under 3.0V. The CT-XTAM521 base reads an incoming voltage below that level as a fault rather than a depleted battery. Remove the handset, wait 30 seconds, and reseat it firmly so the cradle contacts make a clean connection. If the error persists, check the cradle contacts for corrosion and clean with a dry cloth before reseating — the base should accept the pack and begin charging once it reads a voltage above 3.0V.