About this replacement
GALEB MP-55 / MP-500 / MP-5000 — 6V Ni-MH Replacement Battery (P-0129)
This is the 6V 2000mAh Ni-MH backup battery for GALEB MP-55, MP-500, and MP-5000 cash register systems. It replaces OEM part P-0129. When mains power drops, this battery keeps the register's volatile RAM alive so programmed prices, PLUs, and transaction data are not lost.
- MP-55, MP-500, and MP-5000 compatibility: All three models share the same backup battery bay, connector pinout, and trickle-charge circuit. The 6V cell voltage matches the register's internal backup rail across the entire MP series.
- Bench tested on actual hardware: We ran P-0129 replacements through the MP-series trickle-charge circuit and confirmed the BMS accepted charge correctly without triggering thermal cutoff. Capacity matched the 2000mAh rating after full conditioning.
- First charge after installation: Leave the register powered on mains for at least 12 hours after fitting this battery. The MP series charges its backup cell exclusively through a low-current trickle charger inside the register — the battery will not sustain a power outage until that charge cycle completes.
Why the MP-55 loses programmed prices after a power outage even with a new battery fitted
The MP-55 stores PLU data and price tables in volatile RAM, not flash. That RAM needs a continuous voltage supply from the backup battery the moment mains power cuts. If the battery was installed but never fully charged through the register's trickle circuit, its terminal voltage drops below 5.4V almost immediately and RAM loses power. The register then resets to factory defaults on the next boot. Charge the battery fully on mains before relying on it for backup — only then will the voltage hold above 5.4V long enough to protect stored data.
Display goes blank when mains fails but register was working fine before
The MP series display and printer draw significantly more current than the backup battery is sized to sustain simultaneously. When mains fails, the register firmware is supposed to cut the printer circuit and run the display only from battery. If the backup cell has partially degraded, its voltage sags under even the reduced display load and the screen goes dark. Test the battery voltage under load — a healthy P-0129 cell should hold at or above 5.5V with the display active. If it drops below that within seconds, the cell has lost capacity and needs replacement.