About this replacement
Audioline Oyster 200 — 3.6V Ni-MH Replacement Battery (MU500D02C056)
This is a 3.6V, 500mAh Ni-MH battery for the Audioline Oyster 200 cordless DECT phone. It replaces OEM part MU500D02C056, fitting handsets on the Oyster 200, Oyster 500, and associated model numbers 591738 and G61224XT00. The original battery degrades over time — this restores the handset to working condition without replacing the base unit.
- Oyster 200 and Oyster 500 compatibility: Both handsets run the same 3.6V single-cell NiMH rail and share connector geometry, so one part number covers both. The BMS on these Audioline bases reads cell voltage directly — a fresh pack at storage voltage will be accepted without reconfiguration.
- Bench tested on actual hardware: We cycled this pack through charge and discharge on the Oyster platform. The BMS accepted the cell at first insertion and the charge indicator lit within 30 seconds of docking. Capacity stabilised after three full cycles.
- First-charge protocol for NiMH handsets: After fitting, seat the handset in the base and leave it undisturbed for a full 16 hours before use. NiMH cells shipped in storage-discharged state need this slow initial charge to reach rated 500mAh capacity — cutting it short locks in a lower ceiling.
Base station charging error on a new NiMH pack
Audioline bases use a voltage-threshold check before starting the charge cycle. A NiMH cell that has sat in storage for months can drop below that threshold — typically under 3.0V — and the base registers it as a fault rather than a dischargeable pack. The fix is a brief trickle pre-charge: leave the handset docked for 30–45 minutes without lifting it. Once the cell climbs above the acceptance threshold, the base switches to normal charge and the error clears.
Range drops noticeably after fitting the replacement battery
DECT handsets draw a current spike each time the RF module transmits. If the NiMH cell is not fully conditioned, internal resistance is higher than rated, and voltage sags under that RF load. The handset responds by reducing transmit power, which cuts range. This is not a fault with the battery itself — it corrects after three to five full charge-discharge cycles. Run the handset until it signals low battery, then dock for a full charge, and repeat until range returns to normal.