Bottom line, Batteries do fail like anything else. Moreover our bikes often go unused for longish periods, especially during the winter. And then just to add to that many of us fit things such as Trackers, CanSmarts etc. All of which do drain batteries over time. We therefore have two choices when our bikes are idle, disconnect the battery, or put a battery guard/charger on them to keep the battery in good condition.
For what it's worth I have an Optimate charger thats plugged into a fitted SAE plug whenever the bike sits in the garage, hey presto, no battery issues. The SAE plug also doubles up as a convenient power point for heated gear, air pumps etc. As a backup I also carry a Noco Genius Booster battery with a quick plug in tail wired onto the bike battery. When away on trips it doubles up as a USB charger if needed. My previous bike, a K1600 GTL was left in an underground car park for three months, on return the battery had charge, but was insufficient to turn the bike over. The Noco and its plug quickly solved that problem starting her up first time, a two minute job.
Stay safe and well guys ;-)
Tony