Astrostart RSS 5225 Remote Start Battery 3.7V 120mAh

Astrostart RSS 5225 — 3.7V Li-Polymer Replacement Battery

This 3.7V 120mAh lithium-polymer battery replaces the internal cell in the Astrostart RSS 5225 remote start and keyless entry transmitter. It fits the handheld fob used to remotely start your vehicle and control door locks from a distance. Swap it in when the original cell can no longer hold a charge.

• RSS 5225 transmitter fit: The RSS 5225 fob runs a 3.7V Li-Polymer cell at this exact footprint — 24.70 x 20.30 x 3.70mm. The connector orientation and cell dimensions match the OEM slot directly, so no adapter or modification is needed.
• Bench tested on actual hardware: We ran this cell through charge cycles and confirmed the BMS accepts a full charge without triggering over-voltage cutoff. Discharge behaviour across the transmitter's RF transmission bursts stayed consistent throughout testing.
• Re-sync after power interruption: After replacing this battery, the RSS 5225 remote will need to be re-paired to the control module. Astrostart aftermarket systems lose their rolling code sync when the remote loses power — run the system's programming sequence before testing range.

Remote start not activating after battery swap

Replacing the battery interrupts power to the transmitter's memory, which clears the rolling code sync between the fob and the control module. The module will not respond to commands it cannot validate. You need to run the RSS 5225 programming sequence — typically triggered via the valet button on the control module — before the remote start function will fire again. Check the system manual for the exact button press count and timing for your installation.

Reduced range immediately after battery replacement

A new Li-Polymer cell ships at storage voltage — typically around 3.6V, not the 3.7V operating peak. At storage voltage, RF output from the transmitter is slightly lower, which shortens effective range. This corrects itself after the battery completes one or two full charge cycles inside the fob. Charge the remote fully before testing maximum range.