About this replacement
Paradox PCS265LTE — 3.7V Li-Polymer Replacement Battery (1811-020)
This 3.7V 550mAh lithium-polymer cell replaces the internal backup battery in the Paradox PCS265LTE wireless communicator. The PCS265LTE is a compact LTE reporting module used in Paradox security systems to transmit alarm signals over cellular networks. When the original cell degrades, the module loses backup power and can drop off the network during a mains failure.
- PCS265LTE module compatibility: The PCS265LTE uses a single flat lithium-polymer cell on a 3.7V rail. The module's onboard charge circuit expects this exact cell footprint — 43.00 × 24.50 × 5.00mm — and will not seat a thicker cell without damaging the housing.
- Bench tested on actual hardware: We ran this cell through the PCS265LTE charge circuit and confirmed the BMS accepted the cell without fault flags. Charge termination fired correctly at 4.2V and the module reported nominal status to the Paradox panel within the expected window.
- Post-installation float charge requirement: Do not run a zone or comms test immediately after fitting this cell. Allow 24–48 hours on mains power so the module's charge circuit brings the cell to full float voltage. Testing before that window clears will often trigger a false low-battery report on the panel.
Alarm panel showing low battery hours after installing a new cell
The PCS265LTE reports battery status to the Paradox panel based on cell voltage, not just the presence of a cell. A new lithium-polymer cell shipped in partial state of charge will read below the panel's acceptance threshold — typically under 3.9V — and the panel logs a low-battery event. This is not a fault with the cell. Leave the system on mains power for 24–48 hours. Once the cell reaches full float at 4.2V, the panel clears the low-battery condition automatically.
PCS265LTE losing cellular registration during a power cut after battery swap
If the replacement cell has not completed its initial charge cycle, it holds insufficient capacity to sustain the LTE modem through a mains outage. The modem draws a surge current during network re-registration that a partially charged cell cannot support, causing the module to reset mid-outage. The fix is to complete the 48-hour conditioning period on mains before the system faces any power interruption. After full conditioning, confirm the panel shows battery status as normal — not just "present" — before relying on backup.