I suggest like already stated, you don't have enough voltage. If you can't ride it more, hook it to a trickle feed before lashing out unnecessarily on stuff that may not rectify it.
I had a similar thing with my Gutzi when I went from living in the country and had to ride at least a half hour, to stay in Melbourne for a few months.
After a week- wouldn't start, after a couple of misdemeanors, changed headlight from 100/90W, to 60/55, and got in the habit of bump starting- which with even just a half decent battery, is sooooo easy....!
Too many short trips, mostly at night.......