This article applies to ebikes that use the "silverfish battery rail system":
DJ City Bike
DJ Folding Bike
DJ Folding Bike Step Thru
DJ Mountain Bike
Your bike will likely experience intermittent electrical cutout when riding on bumpy or irregular surfaces. A symptom of this is that the battery won't fully insert in the rail, leaving a gap that can be 1/8" (3.5mm) wide:
When you remove the battery, note where the lower end of the battery rail is in relation to the battery socket base. The rail is intended to insert into a slot in the base:
The fix? Loosen the upper mounting bolt on the end of the battery rail, align the lower end of the rail with the mounting slot:
Press down on the rail, fully seating it to the bottom of the battery socket mounting slot:
Put a dab of blue Loctite on the end of the upper mounting screw:
Use a stubby Philips driver to firmly fasten it to the seatstay bridge:
There's also a video of this procedure: