I have a vector 300 amps that will not charge or hold a charge.This is the first time i needed a jump and did not work!It must be a MANUFACTURER DEFECT.What to do? Your Customer

This unit contains a sealed lead acid battery. As such it is necessary to maintain the battery much as you would an RV or tractor or other occasional use battery. If you left the charger plugged in all the time, that's what killed the battery. If you charged it less than once every two or three months, that's what killed the battery. If you stored it in a cold place it may have sulfated. If you stored it in a hot place it may have dried out, especially while charging. The good news is that a replacement battery is not expensive and you can install it yourself. Pull the case apart (look for hidden screws). You may find a good YouTube video to help. Unplug the battery and either shop on-line or go to a battery plus store. But remember, the old SLA battery models like this are rapidly being replaced with LiPoly units that have very good latency (storage) without loss of power. You can get a good one for around $100.