Plantronics 77049-01 Cordless Headset Replacement Battery 2.4V 700mAh

Plantronics Calisto Pro / 77049-01 — 2.4V Ni-MH Replacement Battery

This 2.4V, 700mAh Ni-MH battery replaces the original pack in the Plantronics Calisto Pro and 77049-01 cordless headset. It fits the same footprint at 43.55 × 20.42 × 10.60mm and drops straight into the battery bay without modification. Capacity is rated at 1.68Wh, matching the original specification.

• Calisto Pro and 77049-01 compatibility: Both models run the same 2.4V two-cell NiMH voltage rail and share an identical battery bay and connector orientation. A single pack covers both variants — no adapter or wiring change needed.
• Bench tested on actual hardware: We cycled this pack through charge and discharge on the Calisto Pro base station. The base accepted the new pack without error, the charge indicator lit normally, and the BMS held within the expected 2.4V nominal window across all test cycles.
• First-charge protocol for NiMH headset packs: After installing the new battery, seat the headset in the base and leave it there for a full 16 hours before the first call. NiMH cells shipped from storage are partially discharged — a slow first charge lets them reach rated capacity. Skipping this step typically results in shorter-than-expected talk time for the first few cycles.

Talk time shorter than the original battery after replacement

NiMH cells don't reach full rated capacity on the first charge cycle out of storage. The Calisto Pro's base charger uses a slow trickle charge, so the first three to five cycles will deliver noticeably less talk time than the rated spec. Each full charge-discharge cycle conditions the cells further. By cycle five, the pack should be delivering close to the 700mAh rated capacity.

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

NiMH packs sitting in storage can drop to a voltage the base station's charge controller reads as a fault condition rather than a depleted battery. The base expects to see a pack above roughly 2.0V before it begins a normal charge cycle. If the error light stays on, remove the headset, wait 10 seconds, and re-seat it firmly — this resets the charge controller handshake. If the base still shows an error, leave the headset seated for 30 minutes; the trickle pre-charge circuit should bring the pack voltage up to the acceptance threshold.