Python 7857P Remote Start Compatible Battery 3.7V 70mAh

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

This 3.7V, 70mAh lithium polymer battery replaces the original cell in the Python 7857P wireless remote transmitter. It fits the handheld remote used to activate remote start and control door locks from a distance. Swap it in when the remote stops responding or no longer holds a charge between uses.

• 7857P remote fit: The 7857P transmitter uses a compact LiPo cell on a fixed 3.7V rail. The JFC301819 cell matches the original footprint at 18.50 × 16.40 × 3.80mm, so it seats correctly against the internal contacts without spacers or modification.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a remote transmitter platform. The BMS held stable at 3.7V nominal, with no false low-battery cutoffs during button-press bursts.
• Re-sync the remote after replacement: Python remote start systems require a programming sequence after any power interruption to the transmitter. Once the new battery is in, follow the 7857P sync procedure — enter programming mode via the control module before testing range.

Remote start not activating after battery swap

The 7857P control module communicates with the remote using a rolling code. When the transmitter loses power — even briefly during a battery swap — the rolling code sequence falls out of sync with the module. The remote sends valid signals, but the module rejects them as unrecognised. Run the full Python programming sequence with the transmitter held within one metre of the antenna to re-establish the link.

Alarm triggering when swapping the 7857P battery

Some Python installations treat a sudden power loss at the remote as a tamper event, triggering the vehicle alarm through the control module. This happens because the module loses its periodic check-in signal from the transmitter. Before pulling the old cell, use the system's disarm sequence — typically holding the lock button on the remote or entering the override code — to put the module in a passive state. Restore power with the new battery, then re-sync to exit tamper mode.