EI Compact Cash Register P-1555 Replacement Battery 4.8V 2000mAh

EI Compact Cash Register — 4.8V Ni-MH Replacement Battery (P-1555)

This is a 4.8V, 2000mAh Ni-MH backup battery for the EI Compact P-1555 cash register. It sits inside the register and holds volatile RAM alive when mains power drops, protecting programmed prices, tax rates, and totals. Without a functioning backup cell, any power interruption wipes that data completely.

• P-1555 platform fit: The P-1555 uses a 4-cell Ni-MH pack at 4.8V to match the register's internal trickle charger circuit. Swapping to a different voltage or chemistry trips the charge management logic and can damage the register's charging rail.
• Bench tested on actual hardware: We cycled this pack through the P-1555's trickle charger and confirmed the BMS accepted the charge profile without fault flags. Capacity held at 2000mAh across three discharge cycles on the bench.
• First-install charge requirement: After fitting this battery, leave the register running on mains power for at least 12 hours before testing backup behaviour. The P-1555's trickle charger is low-current by design — the pack will not reach full charge quickly.

Why the P-1555 loses programmed prices after a power outage

The P-1555 stores department prices, PLU data, and tax rates in volatile CMOS RAM — not flash memory. That RAM needs continuous low-level voltage to retain data. When the backup battery is depleted or missing, even a brief mains interruption erases everything. A new battery solves this only after it has received a full charge through the register's internal charger. If the register was unplugged for an extended period before battery replacement, expect a full re-programming cycle once the new pack is charged.

Display goes blank the moment mains power cuts out

The backup battery in the P-1555 is rated to sustain RAM and the real-time clock — not the full display and printer simultaneously. If the display blacks out the instant power cuts, the backup battery is either discharged or has faded below the threshold the register's power controller requires. Check the battery voltage with a multimeter after a 12-hour mains charge — a healthy pack reads between 5.4V and 5.8V fully charged at rest. If the reading is below 4.5V after a full charge cycle, the pack is not recovering and should be replaced.