My original battery (5 years old) still works fine and hammers out 25 mph without a problem, but it has lost a substantial amount of capacity. I charged it all they way up every time I came home, even from a 20 min ride, yet never took it down below 20% to 30%. In the winter months I kept it fully charged, and all it was doing was sitting for five months.
With my new larger capacity battery, I won't charge it so often or as full, and maintain it around 50% in the winter. As far as charging it to 100%, I have read that that is not so harmful if you're going to be using it shortly after it's done charging.