I forgot to plug my battery tender back to the battery after working on the bike and it drained to the point I had one bad cell. I had the same problem as you until I purchased a battery from Brent and made sure It was connected to the tender every time I park the bike.......Angelis

1200CC BIG BORE, W/WISECO PISTONS,.250 STROKED CRANK, PORTED/POLISHED HEADS AND LARGER VALVES, CUSTOM WELDED EXHUAST, DUAL 42MM MIKUNI CARBS.