Aastra Openphone 28 Replacement Battery 2.4V 600mAh

Aastra Openphone 28 — 2.4V Ni-MH Replacement Battery

This is a 2.4V, 600mAh Ni-MH rechargeable battery for the Aastra Openphone 28 cordless handset. It replaces the original pack when the handset no longer holds a charge or drops calls mid-conversation. The cell dimensions are 35.80 × 33.50 × 7.00mm — confirm these against your existing pack before ordering.

• Openphone 28 handset fit: The Openphone 28 uses a 2.4V two-cell Ni-MH configuration. The base station's charging circuit expects this voltage window. A mismatched voltage won't trigger the charge cycle correctly, so stick to the 2.4V spec.
• Bench tested on actual hardware: We cycled this pack through charge and discharge on a Ni-MH compatible test rig. The BMS accepted the charge curve without cutoff errors, and voltage held steady across the full discharge window.
• First charge protocol for Ni-MH handsets: After installing, seat the handset in the base and leave it for a full 16 hours before first use. Ni-MH packs in cordless phones need a slow initial charge to reach rated capacity — a short first charge will leave you with noticeably less talk time from day one.

Talk time shorter than the original battery after replacement

New Ni-MH cells don't deliver full rated capacity on the first cycle. The chemistry needs three to five full charge-discharge cycles before it reaches 600mAh. If talk time feels short in the first few days, that's normal — cycle the battery fully by letting the handset run down, then charging completely in the base. By cycle five, capacity should match the rated spec.

Base station not charging after battery swap

Ni-MH packs that sit in storage can drop to a voltage level the base station's charging circuit won't recognise as a valid battery. The charger sees the low starting voltage and refuses to initiate the charge cycle. To recover, remove the battery, wait 30 seconds, reinsert it firmly, and reseat the handset squarely in the base. If the charge indicator still won't light, the pack voltage may be too low — leave it seated for up to an hour, as some base stations apply a trickle pulse before switching to full charge.