1985 bike, had it for a couple of years, always been reliable. Went to start it 2 weeks ago and the battery was flat, no life at all. I hooked up a trickle charger for a bit and boosted it,rode for 20 min.With engine off, key on, it showed some life at the indicators. I left it parked till today,flat again, not even a glimmer; What is the best procedure for finding a leak? I am assuming the battery is still good. Thanks in advance.