It probably falls into the “costs a shit ton” but some people recommend the fellow carter mug. I’ve never tried it myself, but apparently ceramic-coated insides are best for not affecting the taste of coffee. I think I also saw some kind of ceramic-coated travel mug at Starbucks too? Can’t speak for how spill-proof either of those things are though
Dumb question: did you remember to plug the battery connector back in? Or maybe you damaged that connector? That would explain if it only works when connected to power