You say you jumped it and let it run for 20 miles but did you actually remove it and charge it after? It's my experience that a bike on tickover barely charges a flat battery at all let alone revitalise a totally flat one.
I left my heated grips on for a week on the triumph and when I went out the battery was as much use as a paperweight, I jumped it and the bike ran perfectly, turned it of and again nothing, I took the battery of and put it on my optimate charger and reconditioned it and a year later it's fine.
