Assuming you mean float charging with the onboard convertor/charger that charges the coach batteries. And assuming it used to charge the chassis battery. Your isolation relay or the circuits that control it (B.I.R.D) have failed. You will find a lot of discussion on this forum about it. Search BIRD or battery. If you have a seperate battery charger hooked up, Then your draw is more than the output, or your battery is bad.
Just my 2c
2016 Wildwood 28RLDS
2014 Tundra 1794 Platnum,"23" T-Bucket
2011 Harley Softail, 2010 Spyder RTS