Viper 7857V Remote Start Compatible Battery 3.7V 70mAh

Viper 7857V — 3.7V Li-Polymer Replacement Battery (JFC301819)

This is a 3.7V 70mAh Li-Polymer cell for the Viper 7857V remote transmitter. It replaces the OEM JFC301819 battery inside the 7857V two-way remote used for vehicle remote start, lock, and unlock functions. At 18.50 x 16.40 x 3.80mm, it fits the original housing without modification.

• 7857V remote compatibility: The 7857V uses a small Li-Polymer cell on a low-current draw circuit. Voltage must stay at 3.7V nominal — the remote's microcontroller and RF transmitter both depend on that rail. A mismatched cell voltage causes garbled RF output or no transmission at all.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the bench. The BMS holds the cutoff correctly at low voltage, preventing cell damage from over-discharge during extended storage in a vehicle.
• Post-swap re-sync requirement: After replacing the battery in the 7857V remote, re-sync the transmitter to the Viper control module. Any power interruption to the remote resets its rolling code state — skipping this step leaves the remote unresponsive even with a fully charged cell.

Remote start not activating after battery swap on the 7857V

The 7857V remote communicates with the control module using a rolling code. When the battery is removed, that code state can fall out of sync with the module. The remote may appear to work — LED flashes, buttons respond — but the control module rejects the command. Run the programming sequence in the Viper 7857V install guide to re-pair the remote; the module needs to see the transmitter's ID confirmed before it will action a remote start command.

Reduced range immediately after a fresh battery install

A new Li-Polymer cell ships at storage voltage — typically around 3.6V, not the 3.7V nominal operating level. At storage voltage, the RF transmitter in the 7857V outputs slightly lower power, which cuts effective range. This corrects itself after two or three full charge cycles through the remote's onboard charging circuit. If range stays short after several uses, check that the replacement cell measures at least 3.7V under no-load conditions with a multimeter.