ButterFly 2-in-1 MagSafe Charger very slow charging my Xs Max

My husband got me a ButterFly 2-in-1 MagSafe Charger and it works just fine for my Apple Watch. He specifically asked if it worked for my phone, in fact called me to make sure what phone I had. He was specifically told this was compatible for my phone. Unfortunately, my iPhone XS Max charging is very, very slow. For instance it was on the charger for over 8 hours last night and it went from 20% charged to 52%. The charger and phone were both very warm when I took it off the charger and the charging icon was gray not green indicating it stopped charging at some point. I have taken my cover off to see if that would speed things up. So far, not seeming to make a difference.