About this replacement
Grothe FA64 / FA64-AKKU72 — 9.6V Ni-MH Replacement Battery (39181)
This is a 9.6V, 2000mAh Ni-MH replacement battery for the Grothe FA64 and FA64-AKKU72 wireless alarm system. It fits the transmitters, keypads, and control panel backup positions that use OEM part number 39181. Dimensions are 113.20 x 50.70 x 14.50mm — confirm these against your housing before ordering.
- FA64 and FA64-AKKU72 compatibility: Both models share the same 9.6V Ni-MH cell format and connector pinout. The panel BMS on each reads the same voltage thresholds, so one cell covers both variants without firmware or wiring changes.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the FA64 platform. The BMS accepted the cell without fault codes, and float charge stabilised within the expected window after initial conditioning.
- Post-installation hold period: Do not run a zone or siren test immediately after fitting this cell. Allow 24 to 48 hours on float charge first. Running a diagnostic before the cell reaches full charge can cause the panel to log a low-battery fault that persists until the next full cycle completes.
Alarm panel showing low battery hours after installing the new cell
Ni-MH cells do not arrive at full charge. The FA64 panel reads battery voltage continuously, and a freshly installed cell sitting below the panel's acceptance threshold will trigger a low-battery event almost immediately. This is not a fault with the cell — it is the panel correctly reporting that the cell has not yet reached float. Keep mains power connected and leave the system armed or in standby for 24 to 48 hours. Once the cell reaches approximately 10.5V under float, the panel clears the fault automatically.
Alarm losing saved programming after a mains power outage with new battery fitted
The FA64 panel draws on the backup battery to hold zone programming and system configuration during a mains failure. A new cell that has not completed its conditioning cycle may not deliver enough sustained current to keep the panel memory alive through a longer outage. The panel then reverts to factory defaults when mains is restored, which looks like a programming wipe. Fit the cell, restore mains power, and allow a full 48-hour conditioning period before relying on it for backup — do not test by cutting mains until that window has passed.