Last week when I came back from holidays, my bike wouldn't even click. The battery was already causing issues last winter, so I knew it had to be the battery. But just to be sure, I tried push starting it. And it did start, but the strangest thing happened. Bike started and kept going making all sort of strange sounds. I don't think it was firing in all cylinders. And occasionally it would do a loud pop, loud enough to echo in the neighborhood.
I bought a new Yuasa battery, filled electrolyte, charged overnight with a Yuasa yu-power 900mAmp charger to 13.8v or so, fixed it to the bike everything works flawlessly now. I have the old battery on charger last 3-4 days, but the charger would switch to maintenance mode within seconds (which means the battery is gone I think), and even after 3 days of being on a charger, it only shows 12.4v or so.