Are You sure that Your battery isn't full or almost full, when You try to charge it while hostmode? I'll try to replicate this after my next charging cycle, but message seems quite self-explanatory. Can You post here Your voltage readings, when You got that message? Also, could You try hostmode charging with battery ~50% (or lower, just to be sure)?

I'm glad that You succeed with mounting. Hope that charging will go as well.