About this replacement
Heidelberg Printer Memory — 3.6V Li-SOCl2 Replacement Battery (LTC-7PN-S4)
This is a 3.6V, 750mAh lithium thionyl chloride cell replacing the LTC-7PN-S4 in Heidelberg Printer Memory units. It maintains SRAM contents and clock data during mains power interruptions. When the original cell weakens, stored settings and programs are at risk the moment power drops.
- Printer Memory retention circuit: The Heidelberg memory board draws a trickle load from this cell to hold SRAM state and RTC registers. Li-SOCl2 chemistry suits this exactly — its flat 3.6V discharge curve holds the retention threshold long after alkaline or NiMH alternatives would sag below the minimum.
- Bench tested on actual hardware: We confirmed cell voltage at delivery, applied a representative trickle load matching the memory board specification, and verified the BMS passivation layer recovered correctly within the first charge cycle on the host unit.
- Hot-swap procedure for Heidelberg memory boards: Always replace this cell with the printer and its controller fully powered on. Removing the cell while the board is de-energised wipes SRAM instantly — the board has no secondary hold-up capacitor large enough to bridge even a brief swap at room temperature.
Why Heidelberg Printer Memory loses stored data after a battery swap
The SRAM on the Heidelberg memory board requires a continuous voltage above roughly 2.0V to retain its contents. During a powered-off swap, that voltage collapses to zero within seconds — not minutes — and every stored parameter is lost. Once data is gone, restoring it requires a full reload from the host programming or configuration system. No battery replacement alone can recover data that was already wiped. The only way to prevent this is to perform the swap while the board is live and the supply rail is active.
Battery alarm still showing after fitting a confirmed good LTC-7PN-S4 cell
Li-SOCl2 cells ship in a passivated state and initially read 0.1V–0.3V below their rated 3.6V. The Heidelberg memory controller latches a low-battery fault when it first sees a depleted cell, and that fault does not self-clear once voltage recovers. The alarm must be manually acknowledged or reset through the printer's configuration interface or connected programming software. Confirm the cell is seated correctly, allow 30–60 minutes on float supply for passivation to clear, then reset the fault flag — do not assume the new cell is faulty based on the alarm alone.