I purchased a Bafang kit with a Whale Shark 48volt 20.4 ah Battery. Battery was $699. After just 400 miles the battery wouldn't hold a charge. Tried shipping battery back at local Pack and Ship they wouldn't ship the battery sent me to the UPS store. The UPS store wouldn't ship the battery saying the Watthours was too much making it a large. Told me the only way to ship was by freight line and the cost would be around $500. Disassembled the battery and found one cell with a dark end. removed all cells from the battery the cell with the dark end had a voltage of .86 the other six in parallel read 1.1volts. All other the other 84 cells had a voltage reading of 4.2volts. Looks like one Samsung INR18650-29ea cell went bad ruined all the cells in parallel which in turn ruined the whole battery. $699 battery was good for just 400 miles. I guess you can say it was a lesson well learned.