I have a short commute so about once a month I use my BMW battery charger overnight. It always seems to need charging and sometimes it takes longer than overnight to fully recharge. I am guessing that your battery issues will be solved if you start using a battery charger regularly.
And make sure to buy a smart battery charger that will not overcharge your battery. All of the good ones have the ability to only charge when needed and not to overcharge and harm the battery.
11.5 @123 MPH | JB4 G5 w/WEDGE flash | FBO | RB Turbos | Quaife | Íhlins | Brembo